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Python / Main Program and Working Directory

Check __name__ to Detect Main Program

The entry points into a Python program can be indicated by adding the following code to a Python file:

   if __name__ == '__main__':
       # Main program
       print("In main program")

The __name__ is set to __main__ when the file is being run directly. Otherwise, __name__ is set to the module that was imported, which gives an indication of the scope of the code.

Determine Software and Working Directories

It is often important to understand the working directory (folder) for an application (location where software was run) and the installation location for software. These folders are useful for locating log, input, and output files for software.

Use the following to determine the locations:

# Simple program to illustrate getting important folders

import os

# Main program entry point
if __name__ == '__main__':
    print("")
    print("Current working directory = " + os.getcwd())

    current_file = __file__
    print("Software installation directory = " + os.path.realpath(current_file))

Running the script from the parent folder of the script using Cygwin prints:

$> python3 main-program/get-folders.py

Current working directory = /cygdrive/C/Users/sam/owf-dev/Learn-Python/git-repos/owf-learn-python/mkdocs-project/docs/lang
Software installation directory = /cygdrive/C/Users/sam/owf-dev/Learn-Python/git-repos/owf-learn-python/mkdocs-project/docs/lang/main-program/get-folders.py

Exiting the Program

All programs should exit with an appropriate exit status, which allows calling software (including the operating system) to know whether the program ran successfully. The exit status (or exit code) is an integer. A zero value indicates success, whereas a non-zero value indicates an error and the value indicates the specific error. Exit the program with code similar to:

   # Exit with success status
   exit(0)