Return an iterator over the keys, values or items (represented as tuples of
``(key, value)``) in the dictionary.
- Keys and values are iterated over in an arbitrary order which is non-random,
- varies across Python implementations, and depends on the dictionary's history
- of insertions and deletions. If keys, values and items views are iterated
- over with no intervening modifications to the dictionary, the order of items
- will directly correspond. This allows the creation of ``(value, key)`` pairs
+ Keys and values are iterated over in insertion order.
+ This allows the creation of ``(value, key)`` pairs
using :func:`zip`: ``pairs = zip(d.values(), d.keys())``. Another way to
create the same list is ``pairs = [(v, k) for (k, v) in d.items()]``.
Iterating views while adding or deleting entries in the dictionary may raise
a :exc:`RuntimeError` or fail to iterate over all entries.
+ .. versionchanged:: 3.7
+ Dict order is guaranteed to be insertion order.
+
.. describe:: x in dictview
Return ``True`` if *x* is in the underlying dictionary's keys, values or
>>> print(n)
504
- >>> # keys and values are iterated over in the same order
+ >>> # keys and values are iterated over in the same order (insertion order)
>>> list(keys)
- ['eggs', 'bacon', 'sausage', 'spam']
+ ['eggs', 'sausage', 'bacon', 'spam']
>>> list(values)
[2, 1, 1, 500]
>>> del dishes['eggs']
>>> del dishes['sausage']
>>> list(keys)
- ['spam', 'bacon']
+ ['bacon', 'spam']
>>> # set operations
>>> keys & {'eggs', 'bacon', 'salad'}
assignments, slice assignments, or methods like :meth:`append` and
:meth:`extend`.
-It is best to think of a dictionary as an unordered set of *key: value* pairs,
+It is best to think of a dictionary as a set of *key: value* pairs,
with the requirement that the keys are unique (within one dictionary). A pair of
braces creates an empty dictionary: ``{}``. Placing a comma-separated list of
key:value pairs within the braces adds initial key:value pairs to the
value associated with that key is forgotten. It is an error to extract a value
using a non-existent key.
-Performing ``list(d.keys())`` on a dictionary returns a list of all the keys
-used in the dictionary, in arbitrary order (if you want it sorted, just use
-``sorted(d.keys())`` instead). [2]_ To check whether a single key is in the
+Performing ``list(d)`` on a dictionary returns a list of all the keys
+used in the dictionary, in insertion order (if you want it sorted, just use
+``sorted(d)`` instead). To check whether a single key is in the
dictionary, use the :keyword:`in` keyword.
Here is a small example using a dictionary::
>>> tel = {'jack': 4098, 'sape': 4139}
>>> tel['guido'] = 4127
>>> tel
- {'sape': 4139, 'guido': 4127, 'jack': 4098}
+ {'jack': 4098, 'sape': 4139, 'guido': 4127}
>>> tel['jack']
4098
>>> del tel['sape']
>>> tel['irv'] = 4127
>>> tel
- {'guido': 4127, 'irv': 4127, 'jack': 4098}
- >>> list(tel.keys())
- ['irv', 'guido', 'jack']
- >>> sorted(tel.keys())
+ {'jack': 4098, 'guido': 4127, 'irv': 4127}
+ >>> list(tel)
+ ['jack', 'guido', 'irv']
+ >>> sorted(tel)
['guido', 'irv', 'jack']
>>> 'guido' in tel
True
key-value pairs::
>>> dict([('sape', 4139), ('guido', 4127), ('jack', 4098)])
- {'sape': 4139, 'jack': 4098, 'guido': 4127}
+ {'sape': 4139, 'guido': 4127, 'jack': 4098}
In addition, dict comprehensions can be used to create dictionaries from
arbitrary key and value expressions::
keyword arguments::
>>> dict(sape=4139, guido=4127, jack=4098)
- {'sape': 4139, 'jack': 4098, 'guido': 4127}
+ {'sape': 4139, 'guido': 4127, 'jack': 4098}
.. _tut-loopidioms:
.. [1] Other languages may return the mutated object, which allows method
chaining, such as ``d->insert("a")->remove("b")->sort();``.
-
-.. [2] Calling ``d.keys()`` will return a :dfn:`dictionary view` object. It
- supports operations like membership test and iteration, but its contents
- are not independent of the original dictionary -- it is only a *view*.
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