Python3 Dictionary keys() Method
Python3 DictionaryDescription
The Python3 dictionary keys() method returns a view object.
dict.keys()、dict.values()anddict.items()What is returned is a view object, which provides a dynamic view of the dictionary's entities. This means that when the dictionary changes, the view changes accordingly.
The view object is not a list and does not support indexing. You can use list() to convert it to a list.
We cannot make any modifications to the view object, because dictionary view objects are read-only.
Note:Python2.x directly returns a list.
Syntax
The syntax of the keys() method:
dict.keys()
Parameters
- NA。
Return Value
Returns a view object.
Example
The following example demonstrates how to use the keys() method:
Example
>>> dishes = {'eggs': 2, 'sausage': 1, 'bacon': 1, 'spam': 500}
>>> keys = dishes.keys()
>>> values = dishes.values()
>>> # Iteration
>>> n = 0
>>> for val in values:
... n += val
>>> print(n)
504
>>> # keys and values are iterated in the same order (insertion order)
>>> list(keys) # Use list() to convert to a list
['eggs', 'sausage', 'bacon', 'spam']
>>> list(values)
[2, 1, 1, 500]
>>> # The view object is dynamic and is affected by dictionary changes. In the following example, the dictionary's key is deleted, and the view object, after being converted to a list, also changes accordingly.
>>> del dishes['eggs']
>>> del dishes['sausage']
>>> list(keys)
['bacon', 'spam']
>>> keys = dishes.keys()
>>> values = dishes.values()
>>> # Iteration
>>> n = 0
>>> for val in values:
... n += val
>>> print(n)
504
>>> # keys and values are iterated in the same order (insertion order)
>>> list(keys) # Use list() to convert to a list
['eggs', 'sausage', 'bacon', 'spam']
>>> list(values)
[2, 1, 1, 500]
>>> # The view object is dynamic and is affected by dictionary changes. In the following example, the dictionary's key is deleted, and the view object, after being converted to a list, also changes accordingly.
>>> del dishes['eggs']
>>> del dishes['sausage']
>>> list(keys)
['bacon', 'spam']
Other Extensions