Using python to return a list of squared integers

Question

I'm looking to write a function that takes the integers within a list, such as [1, 2, 3], and returns a new list with the squared integers; [1, 4, 9]

How would I go about this?

PS - just before I was about to hit submit I noticed Chapter 14 of O'Reilly's 'Learning Python' seems to provide the explanation I'm looking for (Pg. 358, 4th Edition)

But I'm still curious to see what other solutions are possible

Answer 1

You can (and should) use list comprehension:

squared = [x**2 for x in lst]

map makes one function call per element and while lambda expressions are quite handy, using map + lambda is mostly slower than list comprehension.

Python Patterns - An Optimization Anecdote is worth a read.

Answer 2

Besides lambda and list comprehensions, you can also use generators. List comprehension calculates all the squares when it's called, generators calculate each square as you iterate through the list. Generators are better when input size is large or when you're only using some initial part of the results.

def generate_squares(a):
    for x in a:
        yield x**2 

# this is equivalent to above
b = (x**2 for x in a)