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Python 3: An interactive deep dive

List Comprehensions

Explore how to use Python 3 list comprehensions to create new lists by applying functions or filtering items from existing lists. Understand how to write compact and readable code that processes lists efficiently, including examples with file manipulation and conditional filtering.

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A list comprehension provides a compact way of mapping a list into another list by applying a function to each of the elements of the list.

Python 3.5
a_list = [1, 9, 8, 4]
print ([elem * 2 for elem in a_list] )          #①
#[2, 18, 16, 8]
print (a_list)                                  #②
#[1, 9, 8, 4]
a_list = [elem * 2 for elem in a_list]          #③
print (a_list)
#[2, 18, 16, 8]

① To make sense of this, look at it from right to left. a_list is the list you’re mapping. The Python interpreter loops through a_list one element at a time, temporarily assigning the value of each element to the variable elem. Python then applies the ...