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概念：
django 中有一个 QueryDict 对象我们可以默认把他看成是一个字典，但是它和一般的字典的不同之处在于:QueryDict 这个字典可以用来处理一个键带有多个值得情况。
即：<QueryDict: {'b': ['3'], 'a': ['1', '2']}>
QueryDict 这个字典支持 get( ) 方法的使用，但是需要区分是一键一值还是一键多值的不同情况
如果是一键一值：
QueryDict.get( key ) 获取的就是当前对应的值(value)
如果是一键多值：
QueryDict.get( key ) 获取的就是最后一个值
QueryDict 还有一个所有值得方法：
QueryDict.getlist( key ) 获取这个键对应的所有值
源码：
首先，在源码中QueryDict是一个类，通过装饰器的作用，实例化出一个QueryDict对象，QueryDict对象可以像操作自己的属性一样来操作QueryDict类中的方法
class QueryDict(MultiValueDict):
"""
A specialized MultiValueDict which represents a query string.
A QueryDict can be used to represent GET or POST data. It subclasses
MultiValueDict since keys in such data can be repeated, for instance
in the data from a form with a <select multiple> field.
By default QueryDicts are immutable, though the copy() method
will always return a mutable copy.
Both keys and values set on this class are converted from the given encoding
(DEFAULT_CHARSET by default) to unicode.
"""
# These are both reset in __init__, but is specified here at the class
# level so that unpickling will have valid values
_mutable = True
_encoding = None
def __init__(self, query_string=None, mutable=False, encoding=None):
super(QueryDict, self).__init__()
if not encoding:
encoding = settings.DEFAULT_CHARSET
self.encoding = encoding
query_string = query_string or ''
parse_qsl_kwargs = {
'keep_blank_values': True,
'fields_limit': settings.DATA_UPLOAD_MAX_NUMBER_FIELDS,
'encoding': encoding,
}
if six.PY3:
if isinstance(query_string, bytes):
# query_string normally contains URL-encoded data, a subset of ASCII.
try:
query_string = query_string.decode(encoding)
except UnicodeDecodeError:
# ... but some user agents are misbehaving :-(
query_string = query_string.decode('iso-8859-1')
for key, value in limited_parse_qsl(query_string, **parse_qsl_kwargs):
self.appendlist(key, value)
else:
for key, value in limited_parse_qsl(query_string, **parse_qsl_kwargs):
try:
value = value.decode(encoding)
except UnicodeDecodeError:
value = value.decode('iso-8859-1')
self.appendlist(force_text(key, encoding, errors='replace'),
value)
self._mutable = mutable
@classmethod
def fromkeys(cls, iterable, value='', mutable=False, encoding=None):
"""
Return a new QueryDict with keys (may be repeated) from an iterable and
values from value.
"""
q = cls('', mutable=True, encoding=encoding)
for key in iterable:
q.appendlist(key, value)
if not mutable:
q._mutable = False
return q
@property
def encoding(self):
if self._encoding is None:
self._encoding = settings.DEFAULT_CHARSET
return self._encoding
@encoding.setter
def encoding(self, value):
self._encoding = value
def _assert_mutable(self):
if not self._mutable:
raise AttributeError("This QueryDict instance is immutable")
def __setitem__(self, key, value):
self._assert_mutable()
key = bytes_to_text(key, self.encoding)
value = bytes_to_text(value, self.encoding)
super(QueryDict, self).__setitem__(key, value)
def __delitem__(self, key):
self._assert_mutable()
super(QueryDict, self).__delitem__(key)
def __copy__(self):
result = self.__class__('', mutable=True, encoding=self.encoding)
for key, value in six.iterlists(self):
result.setlist(key, value)
return result
def __deepcopy__(self, memo):
result = self.__class__('', mutable=True, encoding=self.encoding)
memo[id(self)] = result
for key, value in six.iterlists(self):
result.setlist(copy.deepcopy(key, memo), copy.deepcopy(value, memo))
return result
def setlist(self, key, list_):
self._assert_mutable()
key = bytes_to_text(key, self.encoding)
list_ = [bytes_to_text(elt, self.encoding) for elt in list_]
super(QueryDict, self).setlist(key, list_)
def setlistdefault(self, key, default_list=None):
self._assert_mutable()
return super(QueryDict, self).setlistdefault(key, default_list)
def appendlist(self, key, value):
self._assert_mutable()
key = bytes_to_text(key, self.encoding)
value = bytes_to_text(value, self.encoding)
super(QueryDict, self).appendlist(key, value)
def pop(self, key, *args):
self._assert_mutable()
return super(QueryDict, self).pop(key, *args)
def popitem(self):
self._assert_mutable()
return super(QueryDict, self).popitem()
def clear(self):
self._assert_mutable()
super(QueryDict, self).clear()
def setdefault(self, key, default=None):
self._assert_mutable()
key = bytes_to_text(key, self.encoding)
default = bytes_to_text(default, self.encoding)
return super(QueryDict, self).setdefault(key, default)
def copy(self):
"""Returns a mutable copy of this object."""
return self.__deepcopy__({})
def urlencode(self, safe=None):
"""
Returns an encoded string of all query string arguments.
:arg safe: Used to specify characters which do not require quoting, for
example::
>>> q = QueryDict(mutable=True)
>>> q['next'] = '/a&b/'
>>> q.urlencode()
'next=%2Fa%26b%2F'
>>> q.urlencode(safe='/')
'next=/a%26b/'
"""
output = []
if safe:
safe = force_bytes(safe, self.encoding)
def encode(k, v):
return '%s=%s' % ((quote(k, safe), quote(v, safe)))
else:
def encode(k, v):
return urlencode({k: v})
for k, list_ in self.lists():
k = force_bytes(k, self.encoding)
output.extend(encode(k, force_bytes(v, self.encoding))
for v in list_)
return '&'.join(output)
而QueryDict类又继承自MultiValueDict类，MultiValueDict的具体实现：
class MultiValueDict(dict):
"""
A subclass of dictionary customized to handle multiple values for the
same key.
>>> d = MultiValueDict({'name': ['Adrian', 'Simon'], 'position': ['Developer']})
>>> d['name']
'Simon'
>>> d.getlist('name')
['Adrian', 'Simon']
>>> d.getlist('doesnotexist')
[]
>>> d.getlist('doesnotexist', ['Adrian', 'Simon'])
['Adrian', 'Simon']
>>> d.get('lastname', 'nonexistent')
'nonexistent'
>>> d.setlist('lastname', ['Holovaty', 'Willison'])
This class exists to solve the irritating problem raised by cgi.parse_qs,
which returns a list for every key, even though most Web forms submit
single name-value pairs.
"""
略略略
def dict(self):
"""
Returns current object as a dict with singular values.
"""
return {key: self[key] for key in self}在注释中清楚的描述了，一键一值及一键多值的获取。
在pycharm中试一下：
def index(request):
dict1 = QueryDict('a=1&a=2&b=3')
m = dict1.get('a')
print(dict1)
print(m)
return HttpResponse('it is QueryDict...')
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