List Comprehensions

List Comprehensions is a very powerful tool, which creates a new list based on another list, in a single, readable line.

For example, let's say we need to create a list of integers which specify the length of each word in a certain sentence, but only if the word is not the word "the".

sentence = "the quick brown fox jumps over the lazy dog"
words = sentence.split()
word_lengths = []
for word in words:
     if word != "the":
         word_lengths.append(len(word))
print(words)
print(word_lengths)

Output :

['the', 'quick', 'brown', 'fox', 'jumps', 'over', 'the', 'lazy', 'dog']
[5, 5, 3, 5, 4, 4, 3]

Using a list comprehension, we could simplify this process to this notation:

sentence = "the quick brown fox jumps over the lazy dog"
words = sentence.split()
word_lengths = [len(word) for word in words if word != "the"]
print(words)
print(word_lengths)

Output :

['the', 'quick', 'brown', 'fox', 'jumps', 'over', 'the', 'lazy', 'dog']
[5, 5, 3, 5, 4, 4, 3]