django/utils/maxlength.py

   1 """
   2 Utilities for providing backwards compatibility for the maxlength argument,
   3 which has been replaced by max_length. See ticket #2101.
   4 """
   5
   6 from warnings import warn
   7
   8 def get_maxlength(self):
   9     return self.max_length
  10
  11 def set_maxlength(self, value):
  12     self.max_length = value
  13
  14 def legacy_maxlength(max_length, maxlength):
  15     """
  16     Consolidates max_length and maxlength, providing backwards compatibilty
  17     for the legacy "maxlength" argument.
  18
  19     If one of max_length or maxlength is given, then that value is returned.
  20     If both are given, a TypeError is raised. If maxlength is used at all, a
  21     deprecation warning is issued.
  22     """
  23     if maxlength is not None:
  24         warn("maxlength is deprecated. Use max_length instead.", DeprecationWarning, stacklevel=3)
  25         if max_length is not None:
  26             raise TypeError("Field cannot take both the max_length argument and the legacy maxlength argument.")
  27         max_length = maxlength
  28     return max_length
  29
  30 def remove_maxlength(func):
  31     """
  32     A decorator to be used on a class's __init__ that provides backwards
  33     compatibilty for the legacy "maxlength" keyword argument, i.e.
  34         name = models.CharField(maxlength=20)
  35
  36     It does this by changing the passed "maxlength" keyword argument
  37     (if it exists) into a "max_length" keyword argument.
  38     """
  39     def inner(self, *args, **kwargs):
  40         max_length = kwargs.get('max_length', None)
  41         # pop maxlength because we don't want this going to __init__.
  42         maxlength = kwargs.pop('maxlength', None)
  43         max_length = legacy_maxlength(max_length, maxlength)
  44         # Only set the max_length keyword argument if we got a value back.
  45         if max_length is not None:
  46             kwargs['max_length'] = max_length
  47         func(self, *args, **kwargs)
  48     return inner
  49
  50 # This metaclass is used in two places, and should be removed when legacy
  51 # support for maxlength is dropped.
  52 #   * oldforms.FormField
  53 #   * db.models.fields.Field
  54
  55 class LegacyMaxlength(type):
  56     """
  57     Metaclass for providing backwards compatibility support for the
  58     "maxlength" keyword argument.
  59     """
  60     def __init__(cls, name, bases, attrs):
  61         super(LegacyMaxlength, cls).__init__(name, bases, attrs)
  62         # Decorate the class's __init__ to remove any maxlength keyword.
  63         cls.__init__ = remove_maxlength(cls.__init__)
  64         # Support accessing and setting to the legacy maxlength attribute.
  65         cls.maxlength = property(get_maxlength, set_maxlength)