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.. _multidict-reference:
============
Reference
============
.. module:: multidict
MultiDict
=========
.. class:: MultiDict(**kwargs)
MultiDict(mapping, **kwargs)
MultiDict(iterable, **kwargs)
Creates a mutable multidict instance.
Accepted parameters are the same as for :class:`dict`.
If the same key appears several times it will be added, e.g.::
>>> d = MultiDict([('a', 1), ('b', 2), ('a', 3)])
>>> d
<MultiDict ('a': 1, 'b': 2, 'a': 3)>
.. method:: len(d)
Return the number of items in multidict *d*.
.. method:: d[key]
Return the **first** item of *d* with key *key*.
Raises a :exc:`KeyError` if key is not in the multidict.
.. method:: d[key] = value
Set ``d[key]`` to *value*.
Replace all items where key is equal to *key* with single item
``(key, value)``.
.. method:: del d[key]
Remove all items where key is equal to *key* from *d*.
Raises a :exc:`KeyError` if *key* is not in the map.
.. method:: key in d
Return ``True`` if d has a key *key*, else ``False``.
.. method:: key not in d
Equivalent to ``not (key in d)``
.. method:: iter(d)
Return an iterator over the keys of the dictionary.
This is a shortcut for ``iter(d.keys())``.
.. method:: add(key, value)
Append ``(key, value)`` pair to the dictionary.
.. method:: clear()
Remove all items from the dictionary.
.. method:: copy()
Return a shallow copy of the dictionary.
.. method:: extend([other])
Extend the dictionary with the key/value pairs from *other*,
appending the pairs to this dictionary. For existing keys,
values are added.
Returns ``None``.
:meth:`extend` accepts either another dictionary object or an
iterable of key/value pairs (as tuples or other iterables of
length two). If keyword arguments are specified, the dictionary
is then extended with those key/value pairs:
``d.extend(red=1, blue=2)``.
Effectively the same as calling :meth:`add` for every
``(key, value)`` pair. Also see :meth:`update`, for a version
that replaces existing keys.
.. method:: getone(key[, default])
Return the **first** value for *key* if *key* is in the
dictionary, else *default*.
Raises :exc:`KeyError` if *default* is not given and *key* is not found.
``d[key]`` is equivalent to ``d.getone(key)``.
.. method:: getall(key[, default])
Return a list of all values for *key* if *key* is in the
dictionary, else *default*.
Raises :exc:`KeyError` if *default* is not given and *key* is not found.
.. method:: get(key[, default])
Return the **first** value for *key* if *key* is in the
dictionary, else *default*.
If *default* is not given, it defaults to ``None``, so that this
method never raises a :exc:`KeyError`.
``d.get(key)`` is equivalent to ``d.getone(key, None)``.
.. method:: keys()
Return a new view of the dictionary's keys.
View contains all keys, possibly with duplicates.
.. method:: items()
Return a new view of the dictionary's items (``(key, value)`` pairs).
View contains all items, multiple items can have the same key.
.. method:: values()
Return a new view of the dictionary's values.
View contains all values.
.. method:: popone(key[, default])
If *key* is in the dictionary, remove it and return its the
**first** value, else return *default*.
If *default* is not given and *key* is not in the dictionary, a
:exc:`KeyError` is raised.
.. versionadded:: 3.0
.. method:: pop(key[, default])
An alias to :meth:`popone`
.. versionchanged:: 3.0
Now only *first* occurrence is removed (was all).
.. method:: popall(key[, default])
If *key* is in the dictionary, remove all occurrences and return
a :class:`list` of all values in corresponding order (as
:meth:`getall` does).
If *key* is not found and *default* is provided return *default*.
If *default* is not given and *key* is not in the dictionary, a
:exc:`KeyError` is raised.
.. versionadded:: 3.0
.. method:: popitem()
Remove and return an arbitrary ``(key, value)`` pair from the dictionary.
:meth:`popitem` is useful to destructively iterate over a
dictionary, as often used in set algorithms.
If the dictionary is empty, calling :meth:`popitem` raises a
:exc:`KeyError`.
.. method:: setdefault(key[, default])
If *key* is in the dictionary, return its the **first** value.
If not, insert *key* with a value of *default* and return *default*.
*default* defaults to ``None``.
.. method:: update([other])
Update the dictionary with the key/value pairs from *other*,
overwriting existing keys.
Returns ``None``.
:meth:`update` accepts either another dictionary object or an
iterable of key/value pairs (as tuples or other iterables
of length two). If keyword arguments are specified, the
dictionary is then updated with those key/value pairs:
``d.update(red=1, blue=2)``.
Also see :meth:`extend` for a method that adds to existing keys rather
than update them.
.. seealso::
:class:`MultiDictProxy` can be used to create a read-only view
of a :class:`MultiDict`.
CIMultiDict
===========
.. class:: CIMultiDict(**kwargs)
CIMultiDict(mapping, **kwargs)
CIMultiDict(iterable, **kwargs)
Create a case insensitive multidict instance.
The behavior is the same as of :class:`MultiDict` but key
comparisons are case insensitive, e.g.::
>>> dct = CIMultiDict(a='val')
>>> 'A' in dct
True
>>> dct['A']
'val'
>>> dct['a']
'val'
>>> dct['b'] = 'new val'
>>> dct['B']
'new val'
The class is inherited from :class:`MultiDict`.
.. seealso::
:class:`CIMultiDictProxy` can be used to create a read-only view
of a :class:`CIMultiDict`.
MultiDictProxy
==============
.. class:: MultiDictProxy(multidict)
Create an immutable multidict proxy.
It provides a dynamic view on
the multidict’s entries, which means that when the multidict changes,
the view reflects these changes.
Raises :exc:`TypeError` if *multidict* is not a :class:`MultiDict` instance.
.. method:: len(d)
Return number of items in multidict *d*.
.. method:: d[key]
Return the **first** item of *d* with key *key*.
Raises a :exc:`KeyError` if key is not in the multidict.
.. method:: key in d
Return ``True`` if d has a key *key*, else ``False``.
.. method:: key not in d
Equivalent to ``not (key in d)``
.. method:: iter(d)
Return an iterator over the keys of the dictionary.
This is a shortcut for ``iter(d.keys())``.
.. method:: copy()
Return a shallow copy of the underlying multidict.
.. method:: getone(key[, default])
Return the **first** value for *key* if *key* is in the
dictionary, else *default*.
Raises :exc:`KeyError` if *default* is not given and *key* is not found.
``d[key]`` is equivalent to ``d.getone(key)``.
.. method:: getall(key[, default])
Return a list of all values for *key* if *key* is in the
dictionary, else *default*.
Raises :exc:`KeyError` if *default* is not given and *key* is not found.
.. method:: get(key[, default])
Return the **first** value for *key* if *key* is in the
dictionary, else *default*.
If *default* is not given, it defaults to ``None``, so that this
method never raises a :exc:`KeyError`.
``d.get(key)`` is equivalent to ``d.getone(key, None)``.
.. method:: keys()
Return a new view of the dictionary's keys.
View contains all keys, possibly with duplicates.
.. method:: items()
Return a new view of the dictionary's items (``(key, value)`` pairs).
View contains all items, multiple items can have the same key.
.. method:: values()
Return a new view of the dictionary's values.
View contains all values.
CIMultiDictProxy
================
.. class:: CIMultiDictProxy(multidict)
Case insensitive version of :class:`MultiDictProxy`.
Raises :exc:`TypeError` if *multidict* is not :class:`CIMultiDict` instance.
The class is inherited from :class:`MultiDict`.
Version
=======
All multidicts have an internal version flag. It's changed on every
dict update, thus the flag could be used for checks like cache
expiring etc.
.. function:: getversion(mdict)
Return a version of given *mdict* object (works for proxies also).
The type of returned value is opaque and should be used for
equality tests only (``==`` and ``!=``), ordering is not allowed
while not prohibited explicitly.
.. versionadded:: 3.0
.. seealso:: :pep:`509`
istr
====
:class:`CIMultiDict` accepts :class:`str` as *key* argument for dict
lookups but uses case-folded (lower-cased) strings for the comparison internally.
For more effective processing it should know if the *key* is already
case-folded to skip the :meth:`~str.lower()` call.
The performant code may create
case-folded string keys explicitly hand, e.g::
>>> key = istr('Key')
>>> key
'Key'
>>> mdict = CIMultiDict(key='value')
>>> key in mdict
True
>>> mdict[key]
'value'
For performance :class:`istr` strings should be created once and
stored somewhere for the later usage, see :mod:`aiohttp:aiohttp.hdrs` for example.
.. class:: istr(object='')
istr(bytes_or_buffer[, encoding[, errors]])
Create a new **case-folded** string object from the given
*object*. If *encoding* or *errors* are specified, then the
object must expose a data buffer that will be decoded using the
given encoding and error handler.
Otherwise, returns the result of ``object.__str__()`` (if defined)
or ``repr(object)``.
*encoding* defaults to ``sys.getdefaultencoding()``.
*errors* defaults to ``'strict'``.
The class is inherited from :class:`str` and has all regular
string methods.
.. versionchanged:: 2.0
``upstr()`` is a deprecated alias for :class:`istr`.
.. versionchanged:: 3.7
:class:`istr` doesn't title-case its argument anymore but uses
internal lower-cased data for fast case-insensitive comparison.
Abstract Base Classes
=====================
The module provides two ABCs: ``MultiMapping`` and
``MutableMultiMapping``. They are similar to
:class:`collections.abc.Mapping` and
:class:`collections.abc.MutableMapping` and inherited from them.
.. versionadded:: 3.3
Typing
======
The library is shipped with embedded type annotations, mypy just picks the annotations
by default.
:class:`MultiDict`, :class:`CIMultiDict`, :class:`MultiDictProxy`, and
:class:`CIMultiDictProxy` are *generic* types; please use the corresponding notation for
multidict value types, e.g. ``md: MultiDict[str] = MultiDict()``.
The type of multidict keys is always :class:`str` or a class derived from a string.
.. versionadded:: 3.7
Environment variables
=====================
.. envvar:: MULTIDICT_NO_EXTENSIONS
An environment variable that instructs the packaging scripts to skip
compiling the C-extension based variant of :mod:`multidict`.
When used in runtime, it instructs the pure-Python variant to be imported
from the top-level :mod:`multidict` entry-point package, even when the
C-extension implementation is available.
.. caution::
The pure-Python (uncompiled) version is roughly 20-50 times slower than
its C counterpart, depending on the way it's used.
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