Python Loops Cheat Sheet

Written by Coursera • Updated on

Refresh your memory of Python loop statements and functions with this cheat sheet.

For a more guided walkthrough, check out the resources section at the bottom of this page. Each listed tutorial provides step-by-step directions, examples, and exercises to practice your skills.

4 types of loops in Python

Loop typeExplanation
For loopAn iterating function used to execute statements repeatedly.
While loopUsed to iterate over code when the condition is true. This loop type is typically used when the number of times you’ll need to repeat is unknown.
Nested loopA loop inside of a loop. The innermost loop will execute once for each outer loop iteration.
Do while loopA variant of the while loop that checks the condition at the end of the loop rather than the beginning. The statements inside the loop body will be executed at least once. Python does not have a built-in do while loop but you can modify a while loop to achieve the same functionality.

How to emulate do while loop in Python

A Python while loop only runs when the condition is met. Since it checks that condition at the beginning, it may never run at all. To modify a while loop into a do while loop:

  1. Add True after the keyword while so that the condition is always true to begin with.
  2. Add if statements to check the inside condition and break statements to control the flow of the loop based on your terms.

Here’s an example: Screenshot 2023-02-22 at 11.25.26 AM

Looping in Python

ifif is a common conditional statement. If statements in Python dictate whether a statement should be executed or not by checking for a given condition. If the condition is true, the if block of code will be executed.
elseThe else statement contains the block of code that will execute if the condition from the if statement is false or resolves to zero.
breakA break statement terminates the loop that contains it and redirects the program flow to the following statement.
continueYou can use the keyword continue to end a for loop’s current iteration and continue on to the next.
passIn Python, pass does nothing. It can be used as a placeholder or to disregard code.
range()Python’s range function returns a sequence of numbers. By default, the range starts at 0 and increments in steps of 1.
items()A method of retrieving the key and its corresponding value simultaneously when looping through a dictionary.
list()A list is a mutable sequence type. When used as a function, it takes an iterable and creates a list object.
reversed()reversed() is a built-in Python function that returns a reverse iterator.
enumerate()Enumerate is a built-in function. It adds a counter to an iterable (like a list) and returns it as an enumerate object.

Guidelines for working with Python loops and loop control statements

  • Unlike other programming languages, indentation tells Python which statements are inside or outside of the loop.
  • There are three loop control statements you can use to exit a loop in Python: break, continue, and pass.
  • Any object that can return one member of its group at a time is an iterable object in Python.
  • There is no do while loop in Python, but you can modify a while loop to achieve the same functionality.
  • Use the enumerate function when you need to loop over an iterable while accessing the index of items within it.
  • Use a loop with range to generate number sequences and iterate through them.
  • If a while loop condition never resolves to a false value, you’ll create an infinite loop.


Written by Coursera • Updated on

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