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Python usage notes

Python usage notes

All things assume you have PATH set correctly.

Which versions are available?

Currently, Python versions 3.6 and 3.9 are available, via the python3 and python39 packages, respectively.

Important Note: Performing a yum upgrade operation will not upgrade currently-installed versions of Python to a new major version. This would break existing apps.

1. Installing system-wide packages

Use yum to install any RPM-provided packages that you may use inside your virtual environment.

2. Creating a virtual environment

If using Python 3.9

python3.9 -m venv --system-site-packages /path/to/venv

If using Python 3.6

python3.6 -m venv --system-site-packages /path/to/venv

3. Entering and using the virtual environment

To “enter” a virtual environment, run:

source /path/to/venv/bin/activate

Once completed, you should be able to run the python and pip commands. They will use the version of Python that was used to create the virtual environment.

Which Python command to use outside of a virtual environment?

Python interpreter

Use the versioned python command when feasible. It is always best to run the fully-versioned python command, which is either python3.9 or python3.6, since the python or python3 commands may render different results depending on what packages are installed or what the current environment contains.

Alternatives if python39 is not installed: Use python3.6. One can alternatively use the shorthand python3, but including the major and minor version in the python command is more explicit and is best practice. For instance, launch your python program via:

python3.6 myprogram.py

Alternatives if python39 is installed: Use python3.9 or simply python, since the python39 package creates a python via update-alternatives.

python3.9 myprogram.py

Preferred Installer for Python (pip)

Invoke the Python interpreter command (above), followed by -m pip. For instance:

python3.9 -m pip install --upgrade xlsxwriter

Installing Python packages

See Installing Python Packages

Modules for accessing Db2, RPG, CL etc

  • Be sure to use the itoolkit package from PyPI (installable via pip) for accessing RPG, CL, etc.
  • For database access with odbc:
    • If running on IBM i: Install the python3-pyodbc or python39-pyodbc RPM package, depending on which version of Python you are using. This will be much easier than installing with pip, which will require you to compile these components.
    • If connecting remotely: Install pyodbc through any supported method, and use the IBM i Access ODBC driver.
    • See the ODBC doc for further guidance on ODBC.
  • For database access with ibm_db:
    • If running on IBM i: Install the python3-ibm_db or python39-ibm_db RPM package, depending on which version of Python you are using. DO NOT INSTALL WITH pip!! This will not work.
    • If connecting remotely: Install the ibm_db package in any supported fashion. Db2 Connect licensing is required.