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Python Modules

Python Modules#

So far, we’ve been writing our code all in Jupyter. But when it comes time to write code that we want to reuse, we want to put it into a standalone *.py file.

Then we can load it on in python (or Jupyter) and use the capabilities it provides or make it a standalone program that can be run from the command line.

Tip

Jupyter is great for interactive explorations and sharing your workflow with others in a self-contained way. But if there is an operation that you do over and over, you should put it into a separate module that you import. That way you only need to maintain and debug a single instance of the function, and all your workflows can reuse it.

Editors#

There are a number of popular editors for writing python source. Some popular ones include:

Standalone module#

Here’s a very simply module (lets call it hello.py):

def hello():
    print("hello")

if __name__ == "__main__":
    hello()

There are two ways we can use this.

  • Inside of python (or IPython), we can do:

    import hello
hello.hello()

  • From the command line, we can do:

    python hello.py

Additionally, on a Unix system, we can add:

#!/usr/bin/env python3

to the top and then mark the file as executable, via:

chmod a+x hello.py

allowing us to execute it simply as:

./hello.py

Hint

Here we see how the __name__ variable is treated by python:

  • If we import our module into python, then __name__ is set to the module name

  • If we run the module from the command line, then __name__ is set to __main__

Changing module contents#

If we make changes to our module file, then we need to re-import it. This can be done as:

import importlib
example = importlib.reload(example)
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