Why, when and how to use Context Manager in Python?

Context Manager in Python

In one line, context managers are an efficient way of handling resources in Python. So, what kind of resources are they? It could be any logical resource that you are using for your software, a common one, is database connections, or the files or in few cases, locks for concurrency control.

How exactly Context Manager is efficient?

If we talk about efficient programs, there could be several meanings of it in computer science. For our case, we mean efficient by writing less code, or more specifically, not writing repetitive codes for managing resources. There are some pinpoint benefits of using less repetitive codes other than writing more codes, which is purely technical. You do not forget to perform a step, that is essential if you do it from one source. Let’s find an example. You have a code, that connects to a remote FTP and uploads some content, once done, it closes the connection. If you do the process in several places, you might miss out to close the FTP connection in a place, that is accessed several times by the users. If that is so you might run out of the FTP connection pool on a random day. It is essential to close the connection after you are done with the connection to free the resources. Context Managers can help you write a code, that does the job for you, without the need to remember closing the connection each time.

The ‘with’ statement in Python

Before we can go deeper with Context Managers, we need to learn something about ‘with’ statement in python. ‘with’ is a special statement in python, that does jobs automatically for you. One, it calls a method of setting class, that is called ‘__enter__’ when it calls it, and the other, it automatically calls ‘__exit__’ method when it completes running its code. Let’s do some coding now

with open('test.txt') as f:
    f.write("testing")

In the above code, we are opening a file using the ‘with’ statement of python, then writing some texts in it. But wait, we haven’t closed the file, did you notice? Isn’t it necessary to close a file after opening it to free up the system file descriptors? Absolutely, but using the ‘with’ statement, do it for you even if you don’t do it in your code. In Python, the open() method for opening a file, can be used as Context Manager. For Context Manager, two methods are essential, one is when you set up the call, which is ‘__enter__’ and the other is, when you end the code, that is ‘__exit__’. ‘with’ statement in python is created to be used for Context Managers. As I said, the open() method can be used as Context Manager, which means, Python has both of these methods defined by default with the open() method, and can be used using the ‘with’ statement.

Why and when do we need Context Managers?

Before jumping into, how can we do context managers, let’s understand, if we understand the need of context managers properly with an example! The primary purpose of a context manager is to write cleaner nonrepetitive codes. Do we need this often? Yes, we do. A common example would be in setting up your database connections. If you are setting up a database connection and clean up the things once done, you may create a context manager to do that. There are more complex database use cases of context managers. Let’s focus on one of them. Let’s say, you would like to utilize the database ‘SAVEPOINT’ in a cleaner way, manage the release, and rollback for concurrent transactions based on the savepoint you create dynamically, a clean technique would be to use context manager. Pseudocode could be like the following for this kind of context manager

FUNCTION SAVEPOINT()
    NAME = UUID()
    SQL.EXECUTE('SAVEPOINT ' + UUID)
    TRY
        YIELD
    EXCEPTION
        EXECUTE('ROLLBACK TO SAVEPOINT ' + UUID)
        RAISE
    FINALLY
        EXECUTE('RELEASE SAVEPOINT ' + UUID)

What this context manager is trying to do, is generating a savepoint with a name for you. Once done, it yields the code you instruct it to run after the ‘with’ statement. If you create an exception from those codes, it rollback and sends the exception to the main program else if not it releases the savepoint and gives control to the code after the ‘with’ statement. This is technically the most efficient way of using Savepoint for SQL in your code. Similarly so, we can acquire and release locks for concurrent control using Context managers, or processing an API that had a setup call and an end/cleanup call.

How can we write Context Manager in Python?

There are two ways you can do it. One is using Python class, and the other use, using contextlib and the contextmanager decorator. Let’s first check out, how to do it using Python class to understand the concept better.

First, we want to emulate the way Python uses ‘open’ method as context manager using our own context manager class. A context manager class that can be used using ‘with’ statement could be like the following:

class Open_A_File():
    def __init__(self, name):
        self.name = name

    def __enter__(self):
        self.f = open(self.name)
        return self.f
    
    def __exit__(self, exc_type, exc_val, traceback):
        self.f.close()

with Open_A_File('test.txt') as f:
    f.write('Class Test')

In our class ‘Open_A_File()’, we have 3 methods. Our constructor __init__ method and other two methods are __enter__ and __exit__. When we used Open_A_File() using ‘with’ statement with a parameter, it setup our filename variable for the class using constructor, and then, calls the __enter__ method. It then opens the file and returns the file object. When it returns the file object, we catch it as ‘f’ to use in our code under the ‘with’ statement. We then write the code and the codes within ‘with’ statement ends, hence the __exit__ is automatically called, that closes the file object by calling ‘close()’. We can technically convert any class into a Context Manager and use them using ‘with’ statement if can define the methods to do while entering and exiting the class when called directly with the ‘with’ statement.

Other than class, we can use Context Managers using a function, through the use of contextlib library. This is the most used method of using Context Managers. We used the idea of this, in our pseudocode while demonstrating earlier. Let’s rewrite the above code using contextlib below

from contextlib import contextmanager

@contextmanager
def open_a_fiie(name):
    try:
        f = open(file)
        yield f
    finally:
        f.close()

with Open_A_File('test.txt') as f:
    f.write('Contextlib Test')

We first import contextmanager decorator from contextlib and then, we define a normal function. Although, there exists a ‘yield’ statement. For context managers, the statements that exist before yield would execute on __enter__ method, and the statements after yield would execute on __exit__ method. If you want to return anything to the ‘with’ call, then you need to specify that after yield, as we did in yield f, that means, we returned the file object to the ‘wite’ statement. the yield would replace the code, we run after the ‘with’ statement, like the f.write() in our case.

Hope this make sense. For confusion, or in case you would like to add some, do comment below. Thanks for reading.

Odoo Error – virtual real time limit (151/120s) reached.

There are times, when you might suddenly see your Odoo is shutdown automatically, without warning. Once you enable to logging, you could see an error like the following:

virtual real time limit (151/120s) reached.

or in full details like the following

2021-04-22 06:46:44,054 32685 WARNING ? odoo.service.server: Thread <Thread(odoo.service.http.request.140015617943296, started 140015617943296)> virtual real time limit (151/120s) reached.
2021-04-22 06:46:44,054 32685 INFO ? odoo.service.server: Dumping stacktrace of limit exceeding threads before reloading
2021-04-22 06:46:44,060 32685 INFO ? odoo.tools.misc:
# Thread: <Thread(odoo.service.http.request.140015617943296, started 140015617943296)> (db:n/a) (uid:n/a) (url:n/a)
File: "/opt/rh/rh-python36/root/usr/lib64/python3.6/threading.py", line 884, in _bootstrap
  self._bootstrap_inner()
File: "/opt/rh/rh-python36/root/usr/lib64/python3.6/threading.py", line 916, in _bootstrap_inner
  self.run()
File: "/opt/rh/rh-python36/root/usr/lib64/python3.6/threading.py", line 864, in run
  self._target(*self._args, **self._kwargs)
File: "/opt/rh/rh-python36/root/usr/lib64/python3.6/socketserver.py", line 654, in process_request_thread
  self.finish_request(request, client_address)
File: "/opt/rh/rh-python36/root/usr/lib64/python3.6/socketserver.py", line 364, in finish_request
  self.RequestHandlerClass(request, client_address, self)
File: "/opt/rh/rh-python36/root/usr/lib64/python3.6/socketserver.py", line 724, in __init__
  self.handle()
File: "/opt/odoo/odoo14-venv/lib64/python3.6/site-packages/werkzeug/serving.py", line 329, in handle
  rv = BaseHTTPRequestHandler.handle(self)
File: "/opt/rh/rh-python36/root/usr/lib64/python3.6/http/server.py", line 418, in handle
  self.handle_one_request()
File: "/opt/odoo/odoo14-venv/lib64/python3.6/site-packages/werkzeug/serving.py", line 360, in handle_one_request
  self.raw_requestline = self.rfile.readline()
File: "/opt/rh/rh-python36/root/usr/lib64/python3.6/socket.py", line 586, in readinto
  return self._sock.recv_into(b)
2021-04-22 06:46:44,060 32685 INFO ? odoo.service.server: Initiating server reload

This is because Odoo is killing zombie processes and probably mistakenly crashing your Odoo completely while doing so. The parameter that is used for this purpose, can be found in Odoo documentation:

https://www.odoo.com/documentation/14.0/reference/cmdline.html

--limit-time-real <limit>
Prevents the worker from taking longer than <limit> seconds to process a request. If the limit is exceeded, the worker is killed.

Differs from --limit-time-cpu in that this is a “wall time” limit including e.g. SQL queries.

Defaults to 120.

You may start your service command with something like –limit-time-real 100000 to avoid Odoo from auto killing processes. A command could look like the following if you edit your service file located at:

/etc/systemd/system/odoo14.service

The exec would be like the following:

ExecStart=/usr/bin/scl enable rh-python36 -- /opt/odoo/odoo14-venv/bin/python3 /opt/odoo/odoo14/odoo-bin -c /etc/odoo.conf --limit-time-real=100000

Once the change is done, save the file, and reload the system daemon and restart your Odoo

systemctl daemon-reload
service odoo14 restart

How to Setup Odoo 14 in CentOS 7

Odoo is currently one of the most popular tool for business purposes. It has a community edition, that allows managing ERP at very low cost. Odoo was previously known as OpenERP. Odoo requires to be installed on a dedicated server or VPS. Odoo 14 had come out already. I will have a straight forward how to on installing the latest Odoo 14 in CentOS 7.

Log in to your system and update

First step would be to login to your system and then update the system using yum.

ssh [email protected]_ip

You may check the CentOS version from the redhat release file using the following:

cat /etc/redhat-release

It should show you something like the following if you

CentOS Linux release 7.8.2003 (Core)

Now, you may try updating the system with yum

yum update -y

Once done, now install the EPEL repository as we need it to satisfy a couple of dependecies:

yum install epel-release

Install Python 3.6 packages and Odoo dependencies

We need Python 3.6 at least to run Odoo 14. Odoo 13 also ran on Python 3.6. We will use ‘Software Collection (scl)’ repository to install and use Python 3.6. To find the available Python versions in SCL, you may check the following:

SCL Repository for Python

Now, to install Python 3.6 using SCL, we first need to install the SCL repository for Centos:

yum install centos-release-scl

Once the SCL is loaded, now, you may install the python 3.6 using the following command:

yum install rh-python36

Once the Python is installed, now we will install several tools and packages for Odoo dependencies with the following command:

yum install git gcc nano wget nodejs-less libxslt-devel bzip2-devel openldap-devel libjpeg-devel freetype-devel

Create Odoo User

We now need to create a system user and group for Odoo and define a home directory to /opt/odoo

useradd -m -U -r -d  /opt/odoo -s /bin/bash odoo

You may use any username here, but remember to create the same username for the PostgreSQL as well.

Install PostgreSQL

CentOS base repository unfortunately, comes with Postgresql 9.2. But we want to use PostgreSQL 10 for our Odoo installation. You may check the available PostgreSQL for CentOS 7 using the following command:

yum list postgresql*

As by default CentOS 7 does not provide the PostgreSQL 10, we would use PostgreSQL official repository to download and install the 10 version.

First, we install the Postgres Yum Repository using the following command:

yum install https://download.postgresql.org/pub/repos/yum/10/redhat/rhel-7-x86_64/pgdg-redhat-repo-latest.noarch.rpm

Now, you may install PostgreSQL 10 and related required packages using the following command:

yum install postgresql10 postgresql10-server postgresql10-contrib postgresql10-libs -y

Now, we need to initialize the postgres database and start it. You may do that using the following:

# Initialize the DB
/usr/pgsql-10/bin/postgresql-10-setup initdb

# Start the database
systemctl start postgresql-10.service

If everything goes alright, now you may check the postgresql 10 status:

[[email protected] bin]# systemctl status postgresql-10.service
● postgresql-10.service - PostgreSQL 10 database server
   Loaded: loaded (/usr/lib/systemd/system/postgresql-10.service; disabled; vendor preset: disabled)
   Active: active (running) since Mon 2021-04-05 16:42:15 EDT; 5s ago
     Docs: https://www.postgresql.org/docs/10/static/
  Process: 6380 ExecStartPre=/usr/pgsql-10/bin/postgresql-10-check-db-dir ${PGDATA} (code=exited, status=0/SUCCESS)
 Main PID: 6386 (postmaster)
    Tasks: 8
   Memory: 13.5M
   CGroup: /system.slice/postgresql-10.service
           ├─6386 /usr/pgsql-10/bin/postmaster -D /var/lib/pgsql/10/data/
           ├─6388 postgres: logger process
           ├─6390 postgres: checkpointer process
           ├─6391 postgres: writer process
           ├─6392 postgres: wal writer process
           ├─6393 postgres: autovacuum launcher process
           ├─6394 postgres: stats collector process
           └─6395 postgres: bgworker: logical replication launcher

Now you may enable Postgres to start when booting up using the systemctl enable command:

systemctl enable postgresql-10.service

Now, we need to create a database user for our Odoo installation. You may do that using the following:

su - postgres -c "createuser -s odoo"

Note: If you have created a different user for Odoo installation other than ‘odoo’ than you should change the username here as well.

Install Wkhtmltopdf

Wkhtmltopdf is a open source tool to make html in pdf format so that you may print pdf reports. This tool is used by Odoo and requires to be installed as dependency. CentOS 7 repository does not provide the latest version of this tool, and Odoo requires you to use the latest version. Hence, we require to download the latest version from the Wkhtmltopdf website and install it. To do that, you may first visit the page:

https://wkhtmltopdf.org/downloads.html

The page gives you the direct rpm download link for each version of CentOS/Ubuntu/Mac etc. Download the stable version for CentOS 7. At the time of writing, the URL for CentOS 7 x86_64 bit is the following:

https://github.com/wkhtmltopdf/packaging/releases/download/0.12.6-1/wkhtmltox-0.12.6-1.centos7.x86_64.rpm

You may install this using the following:

cd /opt/
wget https://github.com/wkhtmltopdf/packaging/releases/download/0.12.6-1/wkhtmltox-0.12.6-1.centos7.x86_64.rpm
yum localinstall wkhtmltox-0.12.6-1.centos7.x86_64.rpm

Install and Configure Odoo 14

If you have come all through here, that means you are done with the all dependency installations before starting to download Odoo 14 source code. We will download Odoo 14 from it’s Github repo and use virtualenv to create an isolated python environment to install this python software.

First, login as odoo from root:

su - odoo

Clone the Odoo source code from Github repository:

git clone https://www.github.com/odoo/odoo --depth 1 --branch 14.0 /opt/odoo/odoo14

This will bring the Odoo 14 branch from the Odoo repository and put it inside the folder /opt/odoo/odoo14

Now, we need to enable software collections in order to access python binaries:

scl enable rh-python36 bash

Then we need to create a virtual environment to complete the installation:

cd /opt/odoo
python3 -m venv odoo14-venv

Now, you may activate the virtual environment you have just created:

source odoo14-venv/bin/activate

Now, we upgrade the pip and install the wheel library:

pip install --upgrade pip
pip3 install wheel

Once done, now we can using pip3 to install all the required Python modules from the requirements.txt file:

pip3 install -r odoo14/requirements.txt

Once the installation is complete, now we can deactivate the virtual environment and get back to the root user

deactivate && exit ; exit

If you think, you will create custom modules, you may now create it and give odoo the permission accordingly:

mkdir /opt/odoo/odoo14-custom-addons
chown odoo: /opt/odoo/odoo14-custom-addons

Now, we can fill up the odoo configuration file. First open the odoo.conf file:

nano /etc/odoo.conf

You may paste the following inside:

[options]
; This is the password that allows database operations:
admin_passwd = set_the_password_to_create_odoo_database
db_host = False
db_port = False
db_user = odoo
db_password = False
addons_path = /opt/odoo/odoo14/addons,/opt/odoo/odoo14-custom-addons
; You can enable log file with uncommenting the next line
; logfile = /var/log/odoo14/odoo.log

Please do not forget to change the password ‘set_the_password_to_create_odoo_database’ with a new strong password. This would be used to create Odoo databases from the login screen.

Create the systemd service file and start Odoo 14

Now, we will create a service file, to be able to start, stop and restart Odoo daemon. To do that, first create a service file using the following:

nano /etc/systemd/system/odoo14.service
[Unit]
Description=Odoo14
Requires=postgresql-10.service
After=network.target postgresql-10.service
[Service]
Type=simple
SyslogIdentifier=odoo14
PermissionsStartOnly=true
User=odoo
Group=odoo
ExecStart=/usr/bin/scl enable rh-python36 -- /opt/odoo/odoo14-venv/bin/python3 /opt/odoo/odoo14/odoo-bin -c /etc/odoo.conf
StandardOutput=journal+console
[Install]
WantedBy=multi-user.target

Now, save the file and exit.

Now, you need to reload the systemd daemon to be able to read the latest changes you have made to services. To do that, run:

systemctl daemon-reload

Finally, now we can start Odoo 14 instance using the following command:

systemctl start odoo14

If you are interested to check the status of the instance, you may do this:

systemctl status odoo14

It show green active running, if everything worked out. If you see no error, you may now enable Odoo to start during the boot:

systemctl enable odoo14

If you would like to see the logs, you may either use the journal tools like the following:

journalctl -u odoo14

or uncomment the following line to log the debugs in /etc/odoo.conf

logfile = /var/log/odoo14/odoo.log

After making any change to /etc/odoo.conf, do not forget the restart the Odoo14 instance using systemctl.

Test the Installation


Odoo is currently one of the most popular tool for business purposes. It has a community edition, that allows managing ERP at very low cost. Odoo was previously known as OpenERP. Odoo requires to be installed on a dedicated server or VPS. Odoo 13 had come out on October, 2019. Odoo 14 hasn’t been released yet for production. I will have a straight forward how to on installing the latest Odoo 13 in CentOS 7.

Log in to your system and update

First step would be to login to your system and then update the system using yum.ssh [email protected]_ip

You may check the CentOS version from the redhat release file using the following:cat /etc/redhat-release

It should show you something like the following if youCentOS Linux release 7.8.2003 (Core)

Now, you may try updating the system with yumyum update -y

Once done, now install the EPEL repository as we need it to satisfy a couple of dependecies:yum install epel-release

Install Python 3.6 packages and Odoo dependencies

We need Python 3.6 at least to run Odoo 13. Odoo 12 had support for Python 3.5, unfortunately, Odoo 13 doesn’t. We will use ‘Software Collection (scl)’ repository to install and use Python 3.6. To find the available Python versions in SCL, you may check the following:

SCL Repository for Python

Now, to install Python 3.6 using SCL, we first need to install the SCL repository for Centos:yum install centos-release-scl

Once the SCL is loaded, now, you may install the python 3.6 using the following command:yum install rh-python36

Once the Python is installed, now we will install several tools and packages for Odoo dependencies with the following command:yum install git gcc nano wget nodejs-less libxslt-devel bzip2-devel openldap-devel libjpeg-devel freetype-devel

Create Odoo User

We now need to create a system user and group for Odoo and define a home directory to /opt/odoouseradd -m -U -r -d /opt/odoo -s /bin/bash odoo

You may use any username here, but remember to create the same username for the PostgreSQL as well.

Install PostgreSQL

CentOS base repository unfortunately, comes with Postgresql 9.2. But we want to use PostgreSQL 9.6 for our Odoo installation. You may check the available PostgreSQL for CentOS 7 using the following command:yum list postgresql*

As by default CentOS 7 does not provide the PostgreSQL 9.6, we would use PostgreSQL official repository to download and install the 9.6 version.

First, we install the Postgres Yum Repository using the following command:yum install https://download.postgresql.org/pub/repos/yum/9.6/redhat/rhel-7-x86_64/pgdg-redhat-repo-latest.noarch.rpm

Now, you may install PostgreSQL 9.6 and related required packages using the following command:yum install postgresql96 postgresql96-server postgresql96-contrib postgresql96-libs

Now, we need to initialize the postgres database and start it. You may do that using the following:# Initialize the DB/usr/pgsql-9.6/bin/postgresql96-setup initdb# Start the databasesystemctl start postgresql-9.6.service

Now you may enable Postgres to start when booting up using the systemctl enable command:systemctl enable postgresql-9.6.service

Now, we need to create a database user for our Odoo installation. You may do that using the following:su – postgres -c “createuser -s odoo”

Note: If you have created a different user for Odoo installation other than ‘odoo’ than you should change the username here as well.

Install Wkhtmltopdf

Wkhtmltopdf is a open source tool to make html in pdf format so that you may print pdf reports. This tool is used by Odoo and requires to be installed as dependency. CentOS 7 repository does not provide the latest version of this tool, and Odoo requires you to use the latest version. Hence, we require to download the latest version from the Wkhtmltopdf website and install it. To do that, you may first visit the page:https://wkhtmltopdf.org/downloads.html

The page gives you the direct rpm download link for each version of CentOS/Ubuntu/Mac etc. Download the stable version for CentOS 7. At the time of writing, the URL for CentOS 7 x86_64 bit is the following:https://github.com/wkhtmltopdf/packaging/releases/download/0.12.6-1/wkhtmltox-0.12.6-1.centos7.x86_64.rpm

You may install this using the following:cd /opt/wget https://github.com/wkhtmltopdf/packaging/releases/download/0.12.6-1/wkhtmltox-0.12.6-1.centos7.x86_64.rpmyum localinstall wkhtmltox-0.12.6-1.centos7.x86_64.rpm

Install and Configure Odoo 13

If you have come all through here, that means you are done with the all dependency installations before starting to download Odoo 13 source code. We will download Odoo 13 from it’s Github repo and use virtualenv to create an isolated python environment to install this python software.

First, login as odoo from root:su – odoo

Clone the Odoo source code from Github repository:git clone https://www.github.com/odoo/odoo –depth 1 –branch 13.0 /opt/odoo/odoo13

This will bring the Odoo 13 branch from the Odoo repository and put it inside the folder /opt/odoo/odoo13

Now, we need to enable software collections in order to access python binaries:scl enable rh-python36 bash

Then we need to create a virtual environment to complete the installation:cd /opt/odoopython3 -m venv odoo13-venv

Now, you may activate the virtual environment you have just created:source odoo13-venv/bin/activate

Now, we upgrade the pip and install the wheel library:pip install –upgrade pippip3 install wheel

Once done, now we can using pip3 to install all the required Python modules from the requirements.txt file:pip3 install -r odoo13/requirements.txt

Once the installation is complete, now we can deactivate the virtual environment and get back to the root userdeactivate && exit ; exit

If you think, you will create custom modules, you may now create it and give odoo the permission accordingly:mkdir /opt/odoo/odoo13-custom-addonschown odoo: /opt/odoo/odoo13-custom-addons

Now, we can fill up the odoo configuration file. First open the odoo.conf file:nano /etc/odoo.conf

You may paste the following inside:[options]; This is the password that allows database operations:admin_passwd = set_the_password_to_create_odoo_databasedb_host = Falsedb_port = Falsedb_user = odoodb_password = Falseaddons_path = /opt/odoo/odoo13/addons,/opt/odoo/odoo13-custom-addons; You can enable log file with uncommenting the next line; logfile = /var/log/odoo13/odoo.log

Please do not forget to change the password ‘set_the_password_to_create_odoo_database’ with a new strong password. This would be used to create Odoo databases from the login screen.

Create the systemd service file and start Odoo 13

Now, we will create a service file, to be able to start, stop and restart Odoo daemon. To do that, first create a service file using the following:nano /etc/systemd/system/odoo13.service

and paste the following:[Unit]Description=Odoo13Requires=postgresql-9.6.serviceAfter=network.target postgresql-9.6.service[Service]Type=simpleSyslogIdentifier=odoo13PermissionsStartOnly=trueUser=odooGroup=odooExecStart=/usr/bin/scl enable rh-python35 — /opt/odoo/odoo13-venv/bin/python3 /opt/odoo/odoo13/odoo-bin -c /etc/odoo.confStandardOutput=journal+console[Install]WantedBy=multi-user.target

Now, save the file and exit.

Now, you need to reload the systemd daemon to be able to read the latest changes you have made to services. To do that, run:systemctl daemon-reload

Finally, now we can start Odoo 13 instance using the following command:systemctl start odoo13

If you are interested to check the status of the instance, you may do this:systemctl status odoo13[[email protected] ~]# systemctl status odoo13● odoo13.service – Odoo13 Loaded: loaded (/etc/systemd/system/odoo13.service; enabled; vendor preset: disabled) Active: active (running) since Sun 2020-09-13 08:26:46 EDT; 23h ago Main PID: 24502 (scl) CGroup: /system.slice/odoo13.service ├─24502 /usr/bin/scl enable rh-python36 — /opt/odoo/odoo13-venv/bin/python3 /opt/odoo/odoo13/odoo-bin -c /etc/odoo.conf ├─24503 /bin/bash /var/tmp/sclSWH04z └─24507 /opt/odoo/odoo13-venv/bin/python3 /opt/odoo/odoo13/odoo-bin -c /etc/odoo.conf

It show green active running, if everything worked out. If you see no error, you may now enable Odoo to start during the boot:systemctl enable odoo13

If you would like to see the logs, you may either use the journal tools like the following:journalctl -u odoo13

or uncomment the following line to log the debugs in /etc/odoo.conflogfile = /var/log/odoo13/odoo.log

After making any change to /etc/odoo.conf, do not forget the restart the Odoo13 instance using systemctl.

Test the Installation

You may now test the installation using http://your_server_ip:8069. If everything worked, it should come up. If it doesn’t, you may try stopping your ‘firewalld’ to see if firewall is blocking the port or not:

systemctl stop firewalld

At Mellowhost, we provide Odoo installation and configuration assistance for absolute free of charge. If you are willing to try out any of our VPS for Odoo, you may do so and talk with us through the Live chat or the ticket for Odoo assistance.

Furthermore, Good luck.

How to run composer with different PHP versions in Cpanel?

Question:

When we try to run a composer command, like update, we usually do the following:

composer update

Cpanel has multiple PHP binaries, but in this case, we are unable to select a specific PHP binary to use, instead we have to run it with the default one, how to run composer update with a different php binary in cpanel?

Solution

composer binary file, is a phar file. PHAR is necessarily a PHP Archive and usually automatically detect the running php. But as it is essentially written in php, you may explicitly run it with a different php binary, if you want. To run composer with different php binary, first, you need to find the location of composer. You may do so, using the following:

[email protected] [~]# which composer
/opt/cpanel/composer/bin/composer

Cpanel different php binaries are available under the following kind of directory:

/opt/cpanel/ea-phpXX/usr/bin/php

XX is the version number of PHP. So for example if you need to use PHP 7.4, you would need to run using the following:

/opt/cpanel/ea-php74/usr/bin/php

Now, to run composer update along with PHP 7.4 binary, you may do something like the following:

/opt/cpanel/ea-php74/usr/bin/php /opt/cpanel/composer/bin/composer update

First, make sure you are in the directory where you want to install laravel, for example, something like the following:

cd /home/username/public_html

Then, you may run the above command:

/opt/cpanel/ea-php74/usr/bin/php /opt/cpanel/composer/bin/composer update
or in case, you want to to install
/opt/cpanel/ea-php74/usr/bin/php /opt/cpanel/composer/bin/composer install
or may be, you wan to run update with no-scripts
/opt/cpanel/ea-php74/usr/bin/php /opt/cpanel/composer/bin/composer update --no-scripts

When should you use REST over ORM/DBAL to do Database Operations

Some Background Study

Let’s say, you are architecting a scalable software. Obviously, you would utilize some kind of persistent data storage for your production. If you are developing some kind of transactional software like an ERP/Ecommerce, you are probably more focused into a relational database software like MySQL or MSSQL or PostgreSQL.

Now, one common difficulty for every software architect while working with relational databases, is the ‘Object Relational Impedance Mismatch’ problem. The idea is very straightforward. You design and model your software or programming concept based on Objects, while you store your data in relational tables. Now, how do you map them? As these are different data structures, mapping and utilizing them, is a programming difficulty here.

What is ORM?

In the software world, ORM (Object Relational Mapper) is a form of tool, that exist to resolve the problem. It basically is mapping your relational data into object. That allows you to think your software and data both are stored and operated in Objects. As data is not really stored in an Object, hence, ORM creates an abstraction layer to realize the difference to your software. Using ORM for software design is very useful from architectural point of view, because it takes and returns the same kind of data structure, that you use to design/model your software. It becomes easy to perceive the architecture.

How does DBAL fits here?

As ORM creates an abstraction layer for it’s purpose, it can also be called ‘Database Abstraction Layer’. This is merely conceptual. Now, one purpose of DBAL over ORM, is that DBAL creates the abstraction to keep your software independent from database software alone (Most ORM does the same or helps to achieve the same). So, if you use any of MySQL / MSSQL / Oracle SQL / PostgreSQL or any other SQL based DB engine, it will operate on the same syntax and keep your software compatible out of the box.

So, it’s great, then what’s the problem?

It is obviously conceptually great. But there are cases, when it is better not to use ORM/DBAL. One of the architectural sense of creating abstraction layer in software engineering is that, it creates imperative codes for your mapping. Now, what’s the problem with Imperative codes? If you are unware, Imperative programming refers to the style of programming where we are mainly focused on ‘HOW’ to do something. SQL or relational databases are essentially declarative style of programming, who are focused on ‘WHAT’ to do. For example, when we say ‘select * from users’, it directly gives you the data exists in the users table. We do not care about how does it do it, we only care about the results.

There obviously a catch of declarative code is that, it also creates some kind of abstraction, which uses imperative approach, but it’s underline. For example a Loop in Imperative C is obviously much faster than a loop in Imperative Python (Note: Python can be used in declarative way). But if your software’s imperative code is converting a declarative approach to an imperative piece, then sadly it’s going to be slow, sluggish and less able to scale. ORM or DBAL unfortunately suffers the same. ORM creates an abstraction layer or a slow imperative layer to run declarative SQL. Other cons on using ORM is that, it can duplicate or hobble database structure on your business logic as you are no longer thinking declarative, rather imperative while using ORM.

So where does REST fits in?

To have quicker, simpler and futuristic development, no developer is going to plugin RAW SQL codes in their software. An alternative is to use a declarative REST based api, that uses declarative approach for your database with minimal imperative codes. You can run and consume them as a service with the database software alone. Functional programming is closely related to declarative programming, hence for maximizing performance, you might want to choose a REST api tool that is written in some kind of functional programming language or done in a functional way like with Haskell.

Many database software already started giving HTTP as service protocol with the database software alone, that works in declarative approaches. MySQL comes with a MySQL Router API. PostgreSQL has a solid pREST written in Haskell available in Github. As C# can be written in declarative approach same like Python, there are numerous declarative REST tools written in C# for MSSQL/SQL.

Conclusion

Consuming Declarative API is more like a frontend topic these days since Javascript is taking more functional and declarative futures. React wants you to write codes in declarative approaches, and provides more tools in coming releases with declarative helpers. It is still an odd idea to utilize declarative programming to solve a long existing problem with Object Relational Impedance Mismatch. But then, in the era of millions of users, a declarative database access tool, can cut down a huge amount of cost for infrastructure.

How To Find : If two different date ranges intersects

I was making a Odoo module today, it had a requirement to find the products that has offering within two ranges. Each of the product has different range for discounts/offers. It is sort of like the following:

For example, a shampoo discount starts from 01-06-2020 and ends at 20-06-2020, while another product like a soap discount starts from 10-06-2020 and ends at 22-06-2020. Now if I look for discounted credit notes to apply within a range, then we need to provide some time range, that these ranges intersect. For example, if I want to find discounts that were given within 02-06-2020 – 11 – 06 – 2020, then we should get both the discounts available here, as the discounts were still available for a day to the Soap and a few days for Shampoo. That means, we need to find if any of the given two ranges intersects with the ranges we have discounts for.

The easiest way to calculate this, is to check which date is max among the lower boundaries and which date is minimum in the lower boundaries. This should follow that the starting date would be less than or equal to the ending date, but never greater than the ending date. If greater than, then it does not intersect logically. In python, we can do this like the following:

# first we find all the vendor discounts, it has property start_date and end_date
vendor_discounts = self.env['vendor.discount'].search([])

# list to keep the vendor discount instances
vendor_discount_id_in_range = []

# from the form, we get date_from and date_to, where the dates intersect
for vendor_discount in vendor_discounts:
   # here is the logic to find intersects
    if max(self.date_from, vendor_discount.start_date) <= min(self.date_to, vendor_discount.end_date):
        vendor_discount_id_in_range.append(vendor_discount.id)

So, the logic going to be like the following:

if max(input_date_from, start_date_to_match) <= min(input_date_to, end_date_to_match)

How to Enable Logging in Odoo

There are two ways to see the Odoo Logs. One is rough and can be used to see the latest Odoo logs, it’s the Journal tools. You may do this using the following if your Odoo service is installed as odoo13 for example

journalctl -u odoo13

Note: If you are having trouble primarily in installing Odoo properly, you may check the following:

The other way, is the enable logging to a file. This has to be enabled from the odoo.conf file which is located under /etc/ folder. First we open the /etc/odoo.conf file:

nano /etc/odoo.conf

Now, search to see if you have a directive called ‘logfile’. If you don’t, you may add the following to /etc/odoo.conf:

logfile = /var/log/odoo13/odoo.log

If you already have the directive, but commented out, like this:

; logfile = /var/log/odoo13/odoo.log

You may remove the ‘;’ in front of the logfile directive and save the file. Now you may restart your Odoo instance to allow odoo log the information to the file /var/log/odoo13/odoo.log

systemctl restart odoo13

If the restart showing some errors, probably because it is failing to put permission to odoo13 folder. You may try the following:

mkdir /var/log/odoo13
chown -Rf odoo:odoo /var/log/odoo13
systemctl restart odoo13

How to Install Odoo 13 in CentOS 7

Odoo is currently one of the most popular tool for business purposes. It has a community edition, that allows managing ERP at very low cost. Odoo was previously known as OpenERP. Odoo requires to be installed on a dedicated server or VPS. Odoo 13 had come out on October, 2019. Odoo 14 hasn’t been released yet for production. I will have a straight forward how to on installing the latest Odoo 13 in CentOS 7.

Log in to your system and update

First step would be to login to your system and then update the system using yum.

ssh [email protected]_ip

You may check the CentOS version from the redhat release file using the following:

cat /etc/redhat-release

It should show you something like the following if you

CentOS Linux release 7.8.2003 (Core)

Now, you may try updating the system with yum

yum update -y

Once done, now install the EPEL repository as we need it to satisfy a couple of dependecies:

yum install epel-release

Install Python 3.6 packages and Odoo dependencies

We need Python 3.6 at least to run Odoo 13. Odoo 12 had support for Python 3.5, unfortunately, Odoo 13 doesn’t. We will use ‘Software Collection (scl)’ repository to install and use Python 3.6. To find the available Python versions in SCL, you may check the following:

SCL Repository for Python

Now, to install Python 3.6 using SCL, we first need to install the SCL repository for Centos:

yum install centos-release-scl

Once the SCL is loaded, now, you may install the python 3.6 using the following command:

yum install rh-python36

Once the Python is installed, now we will install several tools and packages for Odoo dependencies with the following command:

yum install git gcc nano wget nodejs-less libxslt-devel bzip2-devel openldap-devel libjpeg-devel freetype-devel

Create Odoo User

We now need to create a system user and group for Odoo and define a home directory to /opt/odoo

useradd -m -U -r -d  /opt/odoo -s /bin/bash odoo

You may use any username here, but remember to create the same username for the PostgreSQL as well.

Install PostgreSQL

CentOS base repository unfortunately, comes with Postgresql 9.2. But we want to use PostgreSQL 9.6 for our Odoo installation. You may check the available PostgreSQL for CentOS 7 using the following command:

yum list postgresql*

As by default CentOS 7 does not provide the PostgreSQL 9.6, we would use PostgreSQL official repository to download and install the 9.6 version.

First, we install the Postgres Yum Repository using the following command:

yum install https://download.postgresql.org/pub/repos/yum/9.6/redhat/rhel-7-x86_64/pgdg-redhat-repo-latest.noarch.rpm

Now, you may install PostgreSQL 9.6 and related required packages using the following command:

yum install postgresql96 postgresql96-server postgresql96-contrib postgresql96-libs

Now, we need to initialize the postgres database and start it. You may do that using the following:

# Initialize the DB
/usr/pgsql-9.6/bin/postgresql96-setup initdb

# Start the database
systemctl start postgresql-9.6.service

Now you may enable Postgres to start when booting up using the systemctl enable command:

systemctl enable postgresql-9.6.service

Now, we need to create a database user for our Odoo installation. You may do that using the following:

su - postgres -c "createuser -s odoo"

Note: If you have created a different user for Odoo installation other than ‘odoo’ than you should change the username here as well.

Install Wkhtmltopdf

Wkhtmltopdf is a open source tool to make html in pdf format so that you may print pdf reports. This tool is used by Odoo and requires to be installed as dependency. CentOS 7 repository does not provide the latest version of this tool, and Odoo requires you to use the latest version. Hence, we require to download the latest version from the Wkhtmltopdf website and install it. To do that, you may first visit the page:

https://wkhtmltopdf.org/downloads.html

The page gives you the direct rpm download link for each version of CentOS/Ubuntu/Mac etc. Download the stable version for CentOS 7. At the time of writing, the URL for CentOS 7 x86_64 bit is the following:

https://github.com/wkhtmltopdf/packaging/releases/download/0.12.6-1/wkhtmltox-0.12.6-1.centos7.x86_64.rpm

You may install this using the following:

cd /opt/
wget https://github.com/wkhtmltopdf/packaging/releases/download/0.12.6-1/wkhtmltox-0.12.6-1.centos7.x86_64.rpm
yum localinstall wkhtmltox-0.12.6-1.centos7.x86_64.rpm

Install and Configure Odoo 13

If you have come all through here, that means you are done with the all dependency installations before starting to download Odoo 13 source code. We will download Odoo 13 from it’s Github repo and use virtualenv to create an isolated python environment to install this python software.

First, login as odoo from root:

su - odoo

Clone the Odoo source code from Github repository:

git clone https://www.github.com/odoo/odoo --depth 1 --branch 13.0 /opt/odoo/odoo13

This will bring the Odoo 13 branch from the Odoo repository and put it inside the folder /opt/odoo/odoo13

Now, we need to enable software collections in order to access python binaries:

scl enable rh-python36 bash

Then we need to create a virtual environment to complete the installation:

cd /opt/odoo
python3 -m venv odoo13-venv

Now, you may activate the virtual environment you have just created:

source odoo13-venv/bin/activate

Now, we upgrade the pip and install the wheel library:

pip install --upgrade pip
pip3 install wheel

Once done, now we can using pip3 to install all the required Python modules from the requirements.txt file:

pip3 install -r odoo13/requirements.txt

Once the installation is complete, now we can deactivate the virtual environment and get back to the root user

deactivate && exit ; exit

If you think, you will create custom modules, you may now create it and give odoo the permission accordingly:

mkdir /opt/odoo/odoo13-custom-addons
chown odoo: /opt/odoo/odoo13-custom-addons

Now, we can fill up the odoo configuration file. First open the odoo.conf file:

nano /etc/odoo.conf

You may paste the following inside:

[options]
; This is the password that allows database operations:
admin_passwd = set_the_password_to_create_odoo_database
db_host = False
db_port = False
db_user = odoo
db_password = False
addons_path = /opt/odoo/odoo13/addons,/opt/odoo/odoo13-custom-addons
; You can enable log file with uncommenting the next line
; logfile = /var/log/odoo13/odoo.log

Please do not forget to change the password ‘set_the_password_to_create_odoo_database’ with a new strong password. This would be used to create Odoo databases from the login screen.

Create the systemd service file and start Odoo 13

Now, we will create a service file, to be able to start, stop and restart Odoo daemon. To do that, first create a service file using the following:

nano /etc/systemd/system/odoo13.service

and paste the following:

[Unit]
Description=Odoo13
Requires=postgresql-9.6.service
After=network.target postgresql-9.6.service

[Service]
Type=simple
SyslogIdentifier=odoo13
PermissionsStartOnly=true
User=odoo
Group=odoo
ExecStart=/usr/bin/scl enable rh-python35 -- /opt/odoo/odoo13-venv/bin/python3 /opt/odoo/odoo13/odoo-bin -c /etc/odoo.conf
StandardOutput=journal+console

[Install]
WantedBy=multi-user.target

Now, save the file and exit.

Now, you need to reload the systemd daemon to be able to read the latest changes you have made to services. To do that, run:

systemctl daemon-reload

Finally, now we can start Odoo 13 instance using the following command:

systemctl start odoo13

If you are interested to check the status of the instance, you may do this:

systemctl status odoo13
[[email protected] ~]# systemctl status odoo13
● odoo13.service - Odoo13
   Loaded: loaded (/etc/systemd/system/odoo13.service; enabled; vendor preset: disabled)
   Active: active (running) since Sun 2020-09-13 08:26:46 EDT; 23h ago
 Main PID: 24502 (scl)
   CGroup: /system.slice/odoo13.service
           ├─24502 /usr/bin/scl enable rh-python36 -- /opt/odoo/odoo13-venv/bin/python3 /opt/odoo/odoo13/odoo-bin -c /etc/odoo.conf
           ├─24503 /bin/bash /var/tmp/sclSWH04z
           └─24507 /opt/odoo/odoo13-venv/bin/python3 /opt/odoo/odoo13/odoo-bin -c /etc/odoo.conf

It show green active running, if everything worked out. If you see no error, you may now enable Odoo to start during the boot:

systemctl enable odoo13

If you would like to see the logs, you may either use the journal tools like the following:

journalctl -u odoo13

or uncomment the following line to log the debugs in /etc/odoo.conf

logfile = /var/log/odoo13/odoo.log

After making any change to /etc/odoo.conf, do not forget the restart the Odoo13 instance using systemctl.

Test the Installation

You may now test the installation using http://your_server_ip:8069. If everything worked, it should come up. If it doesn’t, you may try stopping your ‘firewalld’ to see if firewall is blocking the port or not:

systemctl stop firewalld

At Mellowhost, we provide Odoo installation and configuration assistance for absolute free of charge. If you are willing to try out any of our VPS for Odoo, you may do so and talk with us through the Live chat or the ticket for Odoo assistance.

Furthermore, Good luck.

How to get the string/part/word/text within brackets in Python using Regex

PROBLEM DEFINITION

For example, you have a string like the following:

[lagril] L.A. Girl Pro. Setting HD Matte Finish Spray

While you are scanning the line, you would like to extract the following word from it ‘lagril’, which you are interested in. How to do that?

GETTING TEXT WITHIN BRACKETS USING REGEX IN PYTHON

Our problem falls into a common string extraction problem we face in software engineering. We usually do this using Regular Expressions. Let’s build the regular expression logic first, using regex101.com

We need to find a string that starts with ‘[‘ bracket and ends with ‘]’ bracket, and in the middle, we expect alphanumeric word with small or capital letters, and they can be anything from 0 to any. So, this should be as simple as the following:

\[[A-Za-z0-9]*\]

Now, this should help us target the words that comes within bracket in a sentence/large string. But the trick to grab the text within the bracket is to group them. To use group in regex, we use () brackets without back slash in front. So if the regex is as following:

\[([A-Za-z0-9]*)\]

This will put the matching string in group 1. Now, how can you get what is in the group 1 of a regular expression engine? Let’s dive into python now:

# let's import regular expression engine first
import re

# our string
txt = '[lagril] L.A. Girl Pro. Setting HD Matte Finish Spray'

# our regex search would be as following:
x = re.search(r"\[([A-Za-z0-9]*)\]", txt)

# we know this will put the inner text in group 1. regex object that returned by re.search, has a method called 'group()' to catch the groups matches regex. You may use the following

x.group(1) # prints lagril

Odoo Controller JSON Route Returns 404 – werkzeug.exceptions.NotFound

Even though, if you have defined your routes properly, you are seeing an error of the following:

{
    "id": null,
    "jsonrpc": "2.0",
    "error": {
        "http_status": 404,
        "code": 404,
        "data": {
            "name": "werkzeug.exceptions.NotFound",
            "debug": "Traceback (most recent call last):\n  File \"/opt/odoo/odoo12/odoo/http.py\", line 656, in _handle_exception\n    return super(JsonRequest, self)._handle_exception(exception)\n  File \"/opt/odoo/odoo12/odoo/http.py\", line 314, in _handle_exception\n    raise pycompat.reraise(type(exception), exception, sys.exc_info()[2])\n  File \"/opt/odoo/odoo12/odoo/tools/pycompat.py\", line 87, in reraise\n    raise value\n  File \"/opt/odoo/odoo12/odoo/http.py\", line 1460, in _dispatch_nodb\n    func, arguments = self.nodb_routing_map.bind_to_environ(request.httprequest.environ).match()\n  File \"/opt/odoo/odoo12-venv/lib64/python3.5/site-packages/werkzeug/routing.py\", line 1563, in match\n    raise NotFound()\nwerkzeug.exceptions.NotFound: 404: Not Found\n",
            "message": "404: Not Found",
            "exception_type": "internal_error",
            "arguments": []
        },
        "message": "404: Not Found"
    }
}

This error doesn’t return when you use the http.route as type ‘http’ or default, which is still http, but returns when you use the type ‘json’. One of the cause why the error return is that, you have multiple Odoo databases and Odoo is failing to detect the usable database for the type json. For the type, http, Odoo usually can predict what to use, while for the type json, it can not. For such cases, you would need to use the ‘db-filter’ to add the default database to load for Odoo on the odoo-bin command. If you are using the systemd service file, append the line with the following:

--db-filter=^my_prod$

where ‘my_prod’ is your database name.

So the service ExecStart would look like the following:

ExecStart=/usr/bin/scl enable rh-python35 -- /opt/odoo/odoo12-venv/bin/python3 /opt/odoo/odoo12/odoo-bin -c /etc/odoo.conf --limit-time-real 1009999999 --limit-time-cpu 1009999999 --limit-memory-hard 89179869184000000 --limit-memory-soft 57179869184000000 --db-filter=^my_prod$

After making the change, reload your systemctl and restart your odoo-bin:

systemctl daemon-reload
service odoo12 restart

This should do the job.