Squaring all elements in a list

You could use a list comprehension:

def square(list):    return [i ** 2 for i in list]

Or you could map it:

def square(list):    return map(lambda x: x ** 2, list)

Or you could use a generator. It won't return a list, but you can still iterate through it, and since you don't have to allocate an entire new list, it is possibly more space-efficient than the other options:

def square(list):    for i in list:        yield i ** 2

Or you can do the boring old for-loop, though this is not as idiomatic as some Python programmers would prefer:

def square(list):    ret = []    for i in list:        ret.append(i ** 2)    return ret

Use a list comprehension (this is the way to go in pure Python):

>>> l = [1, 2, 3, 4]>>> [i**2 for i in l][1, 4, 9, 16]

Or numpy (a well-established module):

>>> numpy.array([1, 2, 3, 4])**2array([ 1,  4,  9, 16])

In numpy, math operations on arrays are, by default, executed element-wise. That's why you can **2 an entire array there.

Other possible solutions would be map-based, but in this case I'd really go for the list comprehension. It's Pythonic :) and a map-based solution that requires lambdas is slower than LC.

import numpy as npa = [2 ,3, 4]np.square(a)