Python PIP

In this lesson, we will explore the fundamentals of package management in Python using PIP—the default package manager that is installed automatically with Python. When installing multiple Python versions (for example, Python 2 and Python 3) on the same system, each version comes with its own PIP: pip2 for Python 2 and pip3 for Python 3. Running the PIP command with the -V option displays the associated Python version. Consider the following examples:

python2 -V
pip2 -V
python3 -V
pip3 -V
# pip 9.0.3 from /usr/lib/python3.6/site-packages (python 3.6)

Installing Packages

To install a package with PIP, use the following syntax. For example, installing the popular Flask web framework can be done as:

pip install flask

When Python is installed, a version-specific directory is created under the user library path. Each Python installation maintains its own site-packages folder where packages are stored. For instance, if Flask is installed using pip for Python 2, the installation path might look like this:

• For 32-bit packages
• For 64-bit packages
  • Python 2.7: /usr/lib64/python2.7/site-packages
  • Python 3.6: /usr/lib/python3.6/site-packages

This separation is important for troubleshooting issues where an application cannot locate installed packages. To check where a specific package is installed, use the pip show command:

pip show flask

An example output may be:

Name: Flask
Version: 1.1.1
Summary: A simple framework for building complex web applications.
Home-page: https://palletsprojects.com/p/flask/
Author: Armin Ronacher
Author-email: [email protected]
License: BSD-3-Clause
Location: /usr/lib64/python2.7/site-packages
Requires: Werkzeug, click, Jinja2, itsdangerous

Importing Packages and sys.path

When you import a package using the import statement, Python searches through directories listed in sys.path. To inspect these directories, run:

python2 -c "import sys; print(sys.path)"

This command produces an output similar to:

['/usr/lib/python27.zip',
 '/usr/lib64/python2.7/plat-linux2',
 '/usr/lib/python2.7/lib-tk',
 '/usr/lib/python2.7/lib-old',
 '/usr/lib/python2.7/dylib',
 '/usr/lib/python2.7/site-packages']

If an import fails, reviewing the paths in sys.path can help identify whether the package was installed in a different location or for another Python version.

Managing Dependencies with requirements.txt

For larger applications that require multiple packages, it is common to list all dependencies in a file named requirements.txt. You can then install all dependencies simultaneously by running:

pip install -r requirements.txt

A typical requirements.txt file includes package names along with specific versions to avoid compatibility issues. For example:

Flask==0.10.1
Jinja2==2.7.3
MarkupSafe==0.23
Werkzeug==0.9.6
requests==2.3.0
gunicorn==18.0

Storing dependencies with explicit versions ensures consistency for all developers setting up the project using a single command.

Upgrading and Uninstalling Packages

When a new version of a package becomes available, you can upgrade it using:

pip install flask --upgrade

The upgrade process may produce output similar to:

Installing collected packages: click, flask
Attempting uninstall: flask
Found existing installation: Flask 0.10.1
Uninstalling Flask-0.10.1:
Successfully uninstalled Flask-0.10.1
Successfully installed click-7.1.1 flask-1.1.1

To uninstall a package, run:

pip uninstall package_name

Additional Package Management Tools

Apart from PIP, Python supports other package management tools such as easy_install. Originally, easy_install was used in combination with setuptools to package Python code into a zipped format known as "eggs" (similar to JAR files in Java). Alternatively, you can install or place the egg file in a directory accessible to Python.

Another packaging format is the wheel (with the .whl extension). Unlike eggs, wheels require installation (unpacking) before use. They can be installed with a command like:

pip install app.whl

Summary

Python package management with PIP enables you to install, upgrade, and uninstall packages while managing dependencies through a requirements.txt file. These tools are essential for maintaining a consistent development environment, particularly when working with multiple Python versions or architectures (32-bit vs 64-bit).

Happy coding, and see you in the next lesson!