QueryDict 与重复参数

QueryDict           = <QueryDict: {'a': ['1', '2'], 'b': ['x'], 'tag': ['py', 'django', 'orm'], 'empty': ['']}>
q['a']              = '2'   ← 直接下标取到的是最后一个值
q.get('a')          = '2'
q.getlist('a')      = ['1', '2']
q.getlist('tag')    = ['py', 'django', 'orm']
q.get('missing')    = None  q.get('missing','dflt') = dflt  q.getlist('missing') = []
q.get('empty')      = ''
dict(q)             = {'a': ['1', '2'], 'b': ['x'], 'tag': ['py', 'django', 'orm'], 'empty': ['']}
q.dict()            = {'a': '2', 'b': 'x', 'tag': 'orm', 'empty': ''}   ← 每个 key 只留最后一个值
list(q.items())     = [('a', '2'), ('b', 'x'), ('tag', 'orm'), ('empty', '')]
list(q.lists())     = [('a', ['1', '2']), ('b', ['x']), ('tag', ['py', 'django', 'orm']), ('empty', [''])]
len(q) = 4 (key 的个数,不是参数个数)   q.keys() 顺序 = ['a', 'b', 'tag', 'empty']

q._mutable = False
q['a'] = '3' → AttributeError: This QueryDict instance is immutable
copy() 之后赋值/追加: <QueryDict: {'a': ['3', '4'], 'b': ['x', 'y']}>  getlist("a") = ['3', '4']
urlencode() = a=3&a=4&b=x&b=y
解码后: {'q': ['中文'], 'x': ['a b'], 'y': ['&']}  再 urlencode(): q=%E4%B8%AD%E6%96%87&x=a+b&y=%26
safe 参数保留 "/" : next=/a/b/%3Fc%3D1

request.GET.get("ids")      = 3    getlist = ['1', '2', '3']
int(request.GET["ids"])      = 3 (只取到最后一个)
POST 表单里 ids=[1,2,3]:  getlist = ['1', '2', '3']  get = 3

DATA_UPLOAD_MAX_NUMBER_FIELDS 默认 = 1000
POST 表单 1000 个字段 → request.POST 里 1000 个
POST 表单 1001 个字段 → TooManyFieldsSent: The number of GET/POST parameters exceeded settings.DATA_UPLOAD_MAX_NUMBER_FIELDS.
GET 查询串 1000 个参数 → request.GET 里 1000 个
GET 查询串 1001 个参数 → TooManyFieldsSent: The number of GET/POST parameters exceeded settings.DATA_UPLOAD_MAX_NUMBER_FIELDS.