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Paul Brubaker
14,290 Pointsdict.keys() and dict.values() return view objects, not lists
In the video, it is stated that
dict.keys()
and
dict.values()
return lists, however they actually return view objects that change when the dictionary changes.
sorted(dict.keys())
returns an actual list that does not change when the dictionary changes. This becomes important if whatever is returned is stored with a variable. To illustrate:
>>>course = {'teacher':'Ashley', 'title':'Introducing Dictionaries','level':'Beginner'}
>>>view = course.keys())
>>>view
dict_keys(['teacher', 'title', 'level'])
>>>my_list = sorted(course.keys())
>>>my_list
['level', 'teacher', 'title']
>>>course['student'] = 'Paul'
>>>view
dict_keys(['teacher', 'title', 'level', 'student'])
>>>my_list
['level', 'teacher', 'title']
1 Answer
Chris Freeman
Treehouse Moderator 68,423 PointsCorrect! A dictionary view object were implemented in Python 3.x [see PEP3106 - Revamping dict.keys(), .values() and .items()] as an improvement over the Python 2.x keys(), values(), and items(). The dictionary view object has set-like behavior.
Finding which keys are common to two dictionaries:
>>> d = dict(a=1, b=2, c=3, d=4)
>>> d.keys()
dict_keys(['a', 'b', 'c', 'd'])
>>> d['e'] = 5
>>> d
{'a': 1, 'b': 2, 'c': 3, 'd': 4, 'e': 5}
>>> d.keys()
dict_keys(['a', 'b', 'c', 'd', 'e'])
>>> e = dict(d=1, e=2, f=3, g=4)
>>> e
{'d': 1, 'e': 2, 'f': 3, 'g': 4}
# Find the common keys
>>> d.keys() & e.keys()
{'d', 'e'}
Great Post. Thanks for helping improve the Community!!