comprehensions.md

List, set, and dictonary comprehensions

List comprehensions

Lists avoid the need to make an empty list, do a for loop, and append to the empty list. Instead, it is all done in one line of code.

verbs = ['work', 'eat', 'sleep']
new_list = [element for element in verbs if 'a' in element]
new_list = ['eat']

syntax: created_list = [i for i in old_list if conditional]

original code:

rating_list = []
for movie_dict in user_data["watched"]:
    rating_list.append(movie_dict["rating"])

written as a comprehension

rating_list = [movie_dict["rating"]for movie_dict in user_data["watched"]]

original code:

genre_list = []
for movie_dict in user_data["watched"]:
    genre_list.append(movie_dict["genre"])

written as a comprehension:

genre_list = [movie_dict["genre"] for movie_dict in user_data["watched"]]

original code:

list_of_recommendations = []
    for movie in movies_friends_watched:
        if movie['host'] in user_data['subscriptions']:
            list_of_recommendations.append(movie)

written as a comprehension:

list_of_recommendations = [movie for movie in movies_friends_watched if movie['host'] in user_data['subscriptions']]

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Set comprehensions

new_set = {element for element in iterable (if conditional)}

dictionary comprehensions

new_dictionary = {key:value for(key:value) in old_dict (if conditional)}