2. Dictionary Comprehensions

See docs at: https://docs.python.org/3/tutorial/datastructures.html#list-comprehensions See ref video at: https://www.youtube.com/watch?v=3dt4OGnU5sM

2.1. List comprehension

List comprehensions provide a concise way to create lists.
They are used to make new lists where each element is the result of some operations applied to each member of another sequence or iterable.
They can create a subsequence of those elements that satisfy a certain condition.


new_dictionary = [expression for item in iterable]
  • expression – the item variable only (e.g. x) or any expression such as one that uses the item variable (e.g. x * x).

  • item – a variable.

  • iterable – iterable objects like strings, lists, dictionaries, range function and others.

A list comprehension consists of brackets containing an expression followed by a for clause.
The result will be a new list created by evaluating the expression in the context of the for and if clauses which follow it.
e.g newlist = [2 * n for n in range(5)]

names = ['Lockett', 'Coventry', 'Dunstall']
goals = [1360, 1299, 1254]
print(list(zip(names, goals)))
# {'Lockett': 1360, 'Coventry': 1299, 'Dunstall': 1254}
# I want a dict{'name': 'hero'} for each name, goal in zip(names, goals)
my_dict = {}
for name, goal in zip(names, goals):
    my_dict[name] = goal
# {'Lockett': 1360, 'Coventry': 1299, 'Dunstall': 1254}
my_dict_comprehension = {name: goal for (name, goal) in zip(names, goals)}
my_dict_comprehension = {name: goal for (name, goal) in zip(names, goals) if goal > 1275}
{'Lockett': 1360, 'Coventry': 1299, 'Dunstall': 1254}
{'Lockett': 1360, 'Coventry': 1299}

2.1.1. Practice Questions


  1. Use a list comprehension to create the liset: [(‘A’, ‘X’), (‘A’, ‘Y’), (‘B’, ‘X’), (‘B’, ‘Y’)].

  2. Use a list comprehension to create the liset: [‘AvX’, ‘AvY’, ‘BvX’, ‘BvY’].