For loops

You will probably have met for loops in conjunction with the range function, in simple code like this:

for i in range(5):
    print(i)

This code prints values 0, 1, 2, 3, and 4. It is more or less the Python equivalent of the following C or Java style loop:

for (i = 0; i < 5; i++)
    {
    print(i);
    }

In fact, in Python, loop indices (the variable i) are not used all that often - it might even be considered un-Pythonic. Usually for loops are used to loop directly over a list or other sequence of values.

Pythonic for loops

In this tutorial, we will look at various other techniques available in Python to make your loops shorter and easier to read. The techniques we will cover are:

• Looping over a sequence without using an index variable.
• Looping over a sequence in reverse order using the reversed function.
• Looping over a sequence in sorted order using the sorted function.
• Looping over a sequence with an index using the enumerate function.
• Looping over two or more sequence at a time using the zip function.
• Looping over certain items in sequence with an index using the filter function.

We can use these techniques to loop over sequences of different types, such as:

• Lists.
• Tuples.
• Strings (character by character).
• Sets.
• Dictionaries.

We can also loop over iterables and generators.

Related articles

• List comprehensions
• Objects and variables
• Objects and identity
• Immutable objects
• Global variables
• Data types
• Lists vs tuples
• Sequences
• Named tuples
• Operators
• Short circuit evaluation
• Walrus Operator
• For loop using range vs iterables
• Changing the loop order
• Using enumerate in a for loop
• Using zip in a for loop
• Looping over multiple items (old article)
• Looping over selected items
• Functions
• Declaring functions
• Calling functions
• Function objects and lambdas
• Function decorators
• Exception handling
• With statements
• String functions
• Built-in functions
• Optimisation
• Optimisation good practice
• Low level code optimisation
• Structural optimisation