Reloading Python modules when tinkering with code

importlib.reload is a useful tool you can use within the Python interpreter to test code you are writing in a file. Let’s start by writing a very simple Python script (module), named hello.py:

#! /usr/bin/env python3

def hello(name = "you"):
    print("Hello")

# Always make your script a module with this if statement!
if __name__ == "__main__":
    hello()

Often, when we are working on code in a script, we want test it at the same time from inside the Python interpreter. Let’s open the Python interpreter:

$ python3

and import the hello.py module we just created and try out the hello function (NOTE: you will need to start the python interpreter from within the same folder where you created the hello.py file):

>>> import hello
>>> hello.hello()
Hello

Now, let’s edit our hello function in the hello.py file:

def hello(name = "you"):
    print("Hello,", name)

If we go back to our open Python interpreter and try our hello function again, we will see that the edits we made in the file do not take effect, because we imported the module before making the edits:

>>> hello.hello()
Hello

However, we can use importlib.reload to reload our module and test the edited version of our code:

>>> import importlib
>>> importlib.reload(hello)
>>> hello.hello()
Hello, you
>>> hello.hello("dummy")
Hello, dummy

This allows us to tinker with our code from within the interpreter while we are making edits.