Managing Python Executables and the PATH Environment Variable

Understanding Executable Locations and the PATH

When you install a Python package using pip, the executable files needed to run the programs within that package aren’t automatically added to a system-wide location that your shell (like Bash or Zsh) knows about. This is why you might encounter the "command not found" error after installing a tool like Jupyter Notebook. This tutorial explains why this happens and how to fix it.

What is an Executable?

An executable is a file that your operating system can directly run. When you type a command into your terminal (e.g., jupyter notebook), your shell searches for an executable file with that name.

Where are Executables Installed by pip?

pip typically installs executables into a user-specific directory. The exact location depends on your operating system and Python installation, but a common location is ~/.local/bin. This means the executable is placed in a "bin" (binary) directory within your home directory.

The Role of the PATH Environment Variable

The PATH environment variable is a list of directories that your shell searches through when you enter a command. If an executable with the command name isn’t found in any of the directories listed in PATH, you’ll get the "command not found" error.

Fixing the "Command Not Found" Error

There are several ways to resolve this issue:

1. Direct Execution with python -m: Instead of typing jupyter notebook directly, you can use python -m notebook. This tells Python to run the notebook module within the Jupyter package. This works because Python knows where the packages are installed within its environment. If you used pip3, use python3 -m notebook instead.

2. Adding the Executable Directory to Your PATH (Temporary): You can temporarily add the directory containing the executables to your PATH for the current terminal session. For most systems, this is done with the following command:

   export PATH=$PATH:~/.local/bin
   

   This appends ~/.local/bin to the existing PATH. After running this, you should be able to run jupyter notebook in the same terminal session. This change is not permanent; it will be lost when you close the terminal.

3. Adding the Executable Directory to Your PATH (Permanent): To make the change permanent, you need to add the export PATH=$PATH:~/.local/bin line to your shell’s configuration file. This file is typically .bashrc for Bash, .zshrc for Zsh, or .profile.

   • Editing the Configuration File: Use a text editor (like nano, vim, or gedit) to open the appropriate configuration file. For example:

     nano ~/.bashrc
     

   • Adding the Line: Add the export PATH=$PATH:~/.local/bin line to the end of the file.

   • Saving and Reloading: Save the file and exit the text editor. Then, either close and reopen your terminal, or source the configuration file to reload it:

     source ~/.bashrc
     

   After doing this, the jupyter notebook command should work in all future terminal sessions.

Important Considerations:

• Anaconda/Miniconda: If you’re using Anaconda or Miniconda, the executable directories will be different (typically within your Anaconda installation directory, like ~/anaconda3/bin). Adjust the export PATH command accordingly.
• Multiple Python Installations: If you have multiple Python installations, ensure you’re modifying the configuration file for the correct shell and Python environment.
• sudo and Permissions: Using sudo pip install can sometimes install executables in system-wide locations that require root privileges. While it might appear to fix the issue, it’s generally not recommended as it can lead to permission problems. It’s preferable to manage packages within your user environment.

By understanding the role of the PATH environment variable and how pip installs executables, you can effectively resolve the "command not found" error and ensure that your Python tools are readily available.