List Compehensions
"""
This module shows one-liner comprehensions where we make lists, tuples,
sets and dictionaries by looping through iterators.
"""
def main():
# One interesting fact about data structures is that we can build
# them with comprehensions. Let's explain how the first one works:
# we just want to create zeros so our expression is set to `0`
# since no computing is required; because `0` is a constant value,
# we can set the item that we compute with to `_`; and we want to
# create five zeros so we set the iterator as `range(5)`
assert [0 for _ in range(5)] == [0] * 5 == [0, 0, 0, 0, 0]
# For the next comprehension operations, let's see what we can do
# with a list of 3-5 letter words
words = ["cat", "mice", "horse", "bat"]
# Tuple comprehension can find the length for each word
tuple_comp = tuple(len(word) for word in words)
assert tuple_comp == (3, 4, 5, 3)
# Set comprehension can find the unique word lengths
set_comp = {len(word) for word in words}
assert len(set_comp) < len(words)
assert set_comp == {3, 4, 5}
# Dictionary comprehension can map each word to its length
dict_comp = {word: len(word) for word in words}
assert len(dict_comp) == len(words)
assert dict_comp == {"cat": 3, "mice": 4, "horse": 5, "bat": 3}
if __name__ == "__main__":
main()
Last updated