coding-mentor-agent/kb/python-course-kb-practical-python/wiki/exercises/2-3-some-additional-dictionary-operations.md

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id	source_exercise_id	title	section	source_path	source_repo	source_commit	student_visible_solution	has_private_solution	skip
practical-python-2.3	2.3	Some additional dictionary operations	2.1 Datatypes and Data structures	02_Working_with_data/01_Datatypes.md	https://github.com/dabeaz-course/practical-python	93dca856b41c61a0a0f85ae334116e4c125629ea	false	false	false

Exercise 2.3: Some additional dictionary operations

Source: Practical Python Programming, 02_Working_with_data/01_Datatypes.md.

Exercise 2.3: Some additional dictionary operations

If you turn a dictionary into a list, you’ll get all of its keys:

>>> list(d)
['name', 'shares', 'price', 'date', 'account']
>>>

Similarly, if you use the for statement to iterate on a dictionary, you will get the keys:

>>> for k in d:
        print('k =', k)

k = name
k = shares
k = price
k = date
k = account
>>>

Try this variant that performs a lookup at the same time:

>>> for k in d:
        print(k, '=', d[k])

name = AA
shares = 75
price = 32.2
date = (6, 11, 2007)
account = 12345
>>>

You can also obtain all of the keys using the keys() method:

>>> keys = d.keys()
>>> keys
dict_keys(['name', 'shares', 'price', 'date', 'account'])
>>>

keys() is a bit unusual in that it returns a special dict_keys object.

This is an overlay on the original dictionary that always gives you the current keys—even if the dictionary changes. For example, try this:

>>> del d['account']
>>> keys
dict_keys(['name', 'shares', 'price', 'date'])
>>>

Carefully notice that the 'account' disappeared from keys even though you didn’t call d.keys() again.

A more elegant way to work with keys and values together is to use the items() method. This gives you (key, value) tuples:

>>> items = d.items()
>>> items
dict_items([('name', 'AA'), ('shares', 75), ('price', 32.2), ('date', (6, 11, 2007))])
>>> for k, v in d.items():
        print(k, '=', v)

name = AA
shares = 75
price = 32.2
date = (6, 11, 2007)
>>>

If you have tuples such as items, you can create a dictionary using the dict() function. Try it:

>>> items
dict_items([('name', 'AA'), ('shares', 75), ('price', 32.2), ('date', (6, 11, 2007))])
>>> d = dict(items)
>>> d
{'name': 'AA', 'shares': 75, 'price':32.2, 'date': (6, 11, 2007)}
>>>

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关联来源

• summaries/01_Datatypes