Generators and Generator Expressions in Python

Python Shorts — Part 3

Photo by Chris Ried on Unsplash

In the previous post we looked at iterators. Here, we will showcase generators — which fulfil a similar purpose, but are more convenient to use. Generators are functions returning an iterator, thus we can iterate over them.

For demonstration, let us re-use the example from the previous post, namely generating the first n square numbers. This is done with the following code:

def square(n):
    i = 0
    while (i < n):
        yield i**2
        i += 1

A value is generated and returned every time when reaching the yield statement. The generator can then be used like any other iterator, e.g.:

for x in square(5):
    print(x)

print(sum(square(5)))

Generator Functions

To make things even more convenient, there are generator functions. They are the generator equivalent of list comprehension, and defined by an expression in round brackets, such as: g = (x**2 for x in range(5))

If we inspect g, we see that is a generator object — and we can use it in any function that consumes an Iterable (and naturally also use the generator expression directly):

print(sum(g))
print((x**2 for x in range(5)))

Thanks for reading!

This post is part of a series show-casing important Python concepts quickly. You can find the other parts here:

• Part 1: Lambda Functions in Python
• Part 2: Iterators in Python
• Part 4: Advanced Iteration in Python with enumerate() and zip()
• Part 5: Managing Resources in Python with Context Managers (with statement)
• Part 6: Generating Temporary Files and Directories in Python
• Part 7: Logging in Python
• Part 8: Partial Functions in Python
• Part 9: f-Strings in Python

More content at PlainEnglish.io.

Sign up for our free weekly newsletter. Follow us on Twitter, LinkedIn, YouTube, and Discord.

Interested in scaling your software startup? Check out Circuit.