[GitHub] [airflow] rootcss commented on a change in pull request #10303: Add docs for how airflow manages packages and imports

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rootcss commented on a change in pull request #10303:
URL: https://github.com/apache/airflow/pull/10303#discussion_r476472934



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File path: docs/modules_management.rst
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+ .. Licensed to the Apache Software Foundation (ASF) under one
+    or more contributor license agreements.  See the NOTICE file
+    distributed with this work for additional information
+    regarding copyright ownership.  The ASF licenses this file
+    to you under the Apache License, Version 2.0 (the
+    "License"); you may not use this file except in compliance
+    with the License.  You may obtain a copy of the License at
+
+ ..   http://www.apache.org/licenses/LICENSE-2.0
+
+ .. Unless required by applicable law or agreed to in writing,
+    software distributed under the License is distributed on an
+    "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+    KIND, either express or implied.  See the License for the
+    specific language governing permissions and limitations
+    under the License.
+
+
+
+Modules Management
+==================
+
+Airflow allows you to use your own Python modules in the DAG and in the Airflow configuration. The following article
+will describe how you can create your own module so that Airflow can load it correctly, as well as diagnose problems
+when modules are not loaded properly.
+
+This article is the last one for you if you need to adapt Airflow to the needs of your organization.
+
+Packages Loading in Python
+--------------------------
+
+The list of directories from which Python tries to load the module is given by the variable :any:`sys.path`. Python
+really tries to `intelligently determine the contents of <https://stackoverflow.com/a/38403654>`_ of this variable,
+including depending on the operating system and how Python is installed.
+
+You can check the contents of this variable for the current Python environment by running an interactive terminal as in
+the example below:
+
+.. code-block:: pycon
+
+    >>> import sys
+    >>> from pprint import pprint
+    >>> pprint(sys.path)
+    ['',
+     '/home/arch/.pyenv/versions/3.7.4/lib/python37.zip',
+     '/home/arch/.pyenv/versions/3.7.4/lib/python3.7',
+     '/home/arch/.pyenv/versions/3.7.4/lib/python3.7/lib-dynload',
+     '/home/arch/venvs/airflow/lib/python3.7/site-packages']
+
+``sys.path`` is initialized during program startup. The first precedence is given to the current directory,
+i.e, ``path[0]`` is the directory containing the current script that was used to invoke or an empty string in case
+it was an interactive shell. Second precedence is given to the ``PYTHONPATH`` if provided, followed by installation-dependent
+default paths which is managed by `site <https://docs.python.org/3/library/site.html#module-site>`_ module.
+
+``sys.path`` can also be modified during a Python session by simply using append
+(for example, ``sys.path.append("/path/to/custom/package")``). Python will start searching for packages in the newer
+paths once they're added. Airflow makes use of this feature as described in the further sections.
+
+In the variable ``sys.path`` there is a directory ``site-packages`` which contains the installed **external packages**,
+which means you can install packages with ``pip`` or ``anaconda`` and you can use them in Airflow. In the next section,
+you will learn how to create your own simple installable package and how to specify additional directories to be added
+to ``sys.path`` using the environment variable :envvar:`PYTHONPATH`.
+
+
+Creating a package in Python
+----------------------------
+
+1. Before starting, install the following packages:
+
+``setuptools``: setuptools is a package development process library designed for creating and distributing Python packages.
+
+``wheel``: The wheel package provides a bdist_wheel command for setuptools. It creates .whl file which is directly
+installable through the ``pip install`` command. We can then upload the same file to pypi.org.
+
+.. code-block:: bash
+    pip install --upgrade pip setuptools wheel
+
+2. Create the package directory - in our case, we will call it ``airflow_operators``.
+
+.. code-block:: bash
+    mkdir airflow_operators
+
+3. Create the file ``__init__.py`` inside the package and add following code:
+
+.. code-block:: python
+
+    print("Hello from airflow_operators")
+
+When we import this package, it should print the above message.
+
+4. Create ``setup.py``:
+
+.. code-block:: python
+
+    import setuptools
+
+    setuptools.setup(
+        name='airflow_operators',
+    )
+
+5. Build the wheel:
+
+.. code-block:: bash
+
+    python setup.py bdist_wheel
+
+This will create a few directories in the project and the overall structure will look like following:
+
+.. code-block:: bash
+
+    .
+    ├── airflow_operators
+    │   ├── __init__.py
+    ├── airflow_operators.egg-info
+    │   ├── PKG-INFO
+    │   ├── SOURCES.txt
+    │   ├── dependency_links.txt
+    │   └── top_level.txt
+    ├── build
+    │   └── bdist.macosx-10.15-x86_64
+    ├── dist
+    │   └── airflow_operators-0.0.0-py3-none-any.whl
+    └── setup.py
+
+
+6. Install the .whl file using pip:
+
+.. code-block:: bash
+
+    pip install dist/airflow_operators-0.0.0-py3-none-any.whl
+
+7. The package is now ready to use!
+
+.. code-block:: pycon
+
+  >>> import airflow_operators
+  Hello from airflow_operators
+  >>>
+
+The package can be removed using pip command:
+
+.. code-block:: bash
+
+    pip uninstall airflow_operators
+
+For more details, see: https://packaging.python.org/tutorials/packaging-projects/

Review comment:
       Thank you.




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