Idioms in Python

Idioms in Python helps in performing a range of tasks. As a programmer, you shall learn this module. Learn more about this Python module in this guide.

Idioms in Python: Dictionary key initializations

Prefer dict.get method if you are not sure if the key is present. It allows you to return a default value if key is not found. The traditional method dict[key] would raise a KeyError exception.

Rather than doing

def add_student():
students['count'] += 1
except KeyError:
students['count'] = 1


def add_student():
students[‘count’] = students.get(‘count’, 0) + 1

Switching variables

To switch the value of two variables you can use tuple unpacking.

x = True 
y = False
x, y = y, x

Use truth value testing

Python will implicitly convert any object to a Boolean value for testing, so use it wherever possible.

Good examples, using implicit truth testing if attr:
do something
if not attr:
do something
Bad examples, using specific types if attr == 1:
do something
if attr == True:

do something

if attr != '':
do something
If you are looking to specifically check for None, use 'is' or 'is not' if attr is None:
do something

This generally produces more readable code, and is usually much safer when dealing with unexpected types.

Click here for a list of what will be evaluated to False.

Idioms in Python: Test for “main” to avoid unexpected code execution

It is good practice to test the calling program’s name variable before executing your code.

import sys
def main():
Your code starts here
Don't forget to provide a return code return 0
if name == "main":

Using this pattern ensures that your code is only executed when you expect it to be; for example, when you run your file explicitly:


The benefit, however, comes if you decide to import your file in another program (for example if you are writing it as part of a library). You can then import your file, and the main trap will ensure that no code is executed unexpectedly:

A new program file

import my_program # main() is not run
But you can run main() explicitly if you really want it to run: my_program.main()


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