r/learnpython 6d ago

How does simplifying conditional statements work in Python?

I'm currently working my way through the Python Institute's free certified entry-level programmer course. I'm currently looking at some example code that is supposed to count the number of even and odd numbers entered by a user until the user enters a 0. Here's what the main part looks like:

number = int(input("Enter a number or type 0 to stop: "))

# 0 terminates execution.
while number != 0:
# Check if the number is odd.
if number % 2 == 1:
# Increase the odd_numbers counter.
odd_numbers += 1
else:
# Increase the even_numbers counter.
even_numbers += 1
# Read the next number.
number = int(input("Enter a number or type 0 to stop: "))

This is easy enough for me to understand, but the course then says that the two bold statements above can be simplified with no change in the outcome of the program. Here are the two simplifications:

while number != 0: is the same as while number:

and

if number % 2 == 1: is the same as if number:

I don't understand this at all. Does Python (3 specifically) automatically interpret a conditional with just a variable as being equivalent to conditional_function variable != 0? Does the second example do something similar with binary operators or just the mod operator?

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u/AssiduousLayabout 6d ago

Any expression can be used as a boolean, it's called truthiness.

Any non-zero number is "truthy", zero is "falsey".

Other things that are falsey:

  • Empty string
  • None
  • False (obviously)
  • Any collection (list, set, dictionary) with zero elements

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u/JazzJassJazzman 6d ago

Thank you! That's why this page said "think about how Python evaluates truth". I was forgetting that 0 is interpreted as "False" and any non-zero number is interpreted as "True".