diff options
Diffstat (limited to 'Doc/tutorial')
| -rw-r--r-- | Doc/tutorial/datastructures.rst | 26 |
1 files changed, 11 insertions, 15 deletions
diff --git a/Doc/tutorial/datastructures.rst b/Doc/tutorial/datastructures.rst index b95aca8..7855ef2 100644 --- a/Doc/tutorial/datastructures.rst +++ b/Doc/tutorial/datastructures.rst @@ -497,7 +497,7 @@ You can't use lists as keys, since lists can be modified in place using index 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 @@ -509,9 +509,9 @@ pair with ``del``. If you store using a key that is already in use, the old 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:: @@ -519,16 +519,16 @@ 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 @@ -539,7 +539,7 @@ The :func:`dict` constructor builds dictionaries directly from sequences of 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:: @@ -551,7 +551,7 @@ When the keys are simple strings, it is sometimes easier to specify pairs using keyword arguments:: >>> dict(sape=4139, guido=4127, jack=4098) - {'sape': 4139, 'jack': 4098, 'guido': 4127} + {'sape': 4139, 'guido': 4127, 'jack': 4098} .. _tut-loopidioms: @@ -710,7 +710,3 @@ interpreter will raise a :exc:`TypeError` exception. .. [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*. |