1"""Mixin classes for custom array types that don't inherit from ndarray."""

2 from numpy.core import umath as um

3

4

5__all__ = ['NDArrayOperatorsMixin']

6

7

8 def _disables_array_ufunc(obj):

9 """True when __array_ufunc__ is set to None."""

10 try:

11 return obj.__array_ufunc__ is None

12 except AttributeError:

13 return False

14

15

16 def _binary_method(ufunc, name):

17 """Implement a forward binary method with a ufunc, e.g., __add__."""

18 def func(self, other):

19 if _disables_array_ufunc(other):

20 return NotImplemented

21 return ufunc(self, other)

22 func.__name__ = '__{}__'.format(name)

23 return func

24

25

26 def _reflected_binary_method(ufunc, name):

27 """Implement a reflected binary method with a ufunc, e.g., __radd__."""

28 def func(self, other):

29 if _disables_array_ufunc(other):

30 return NotImplemented

31 return ufunc(other, self)

32 func.__name__ = '__r{}__'.format(name)

33 return func

34

35

36 def _inplace_binary_method(ufunc, name):

37 """Implement an in-place binary method with a ufunc, e.g., __iadd__."""

38 def func(self, other):

39 return ufunc(self, other, out=(self,))

40 func.__name__ = '__i{}__'.format(name)

41 return func

42

43

44 def _numeric_methods(ufunc, name):

45 """Implement forward, reflected and inplace binary methods with a ufunc."""

46 return (_binary_method(ufunc, name),

47 _reflected_binary_method(ufunc, name),

48 _inplace_binary_method(ufunc, name))

49

50

51 def _unary_method(ufunc, name):

52 """Implement a unary special method with a ufunc."""

53 def func(self):

54 return ufunc(self)

55 func.__name__ = '__{}__'.format(name)

56 return func

57

58

59 class NDArrayOperatorsMixin:

60 """Mixin defining all operator special methods using __array_ufunc__.

61

62 This class implements the special methods for almost all of Python's

63 builtin operators defined in the `operator` module, including comparisons

64 (``==``, ``>``, etc.) and arithmetic (``+``, ``*``, ``-``, etc.), by

65 deferring to the ``__array_ufunc__`` method, which subclasses must

66 implement.

67

68 It is useful for writing classes that do not inherit from `numpy.ndarray`,

69 but that should support arithmetic and numpy universal functions like

70 arrays as described in `A Mechanism for Overriding Ufuncs

71 <https://numpy.org/neps/nep-0013-ufunc-overrides.html>`_.

72

73 As an trivial example, consider this implementation of an ``ArrayLike``

74 class that simply wraps a NumPy array and ensures that the result of any

75 arithmetic operation is also an ``ArrayLike`` object::

76

77 class ArrayLike(np.lib.mixins.NDArrayOperatorsMixin):

78 def __init__(self, value):

79 self.value = np.asarray(value)

80

81 # One might also consider adding the built-in list type to this

82 # list, to support operations like np.add(array_like, list)

83 _HANDLED_TYPES = (np.ndarray, numbers.Number)

84

85 def __array_ufunc__(self, ufunc, method, *inputs, **kwargs):

86 out = kwargs.get('out', ())

87 for x in inputs + out:

88 # Only support operations with instances of _HANDLED_TYPES.

89 # Use ArrayLike instead of type(self) for isinstance to

90 # allow subclasses that don't override __array_ufunc__ to

91 # handle ArrayLike objects.

92 if not isinstance(x, self._HANDLED_TYPES + (ArrayLike,)):

93 return NotImplemented

94

95 # Defer to the implementation of the ufunc on unwrapped values.

96 inputs = tuple(x.value if isinstance(x, ArrayLike) else x

97 for x in inputs)

98 if out:

99 kwargs['out'] = tuple(

100 x.value if isinstance(x, ArrayLike) else x

101 for x in out)

102 result = getattr(ufunc, method)(*inputs, **kwargs)

103

104 if type(result) is tuple:

105 # multiple return values

106 return tuple(type(self)(x) for x in result)

107 elif method == 'at':

108 # no return value

109 return None

110 else:

111 # one return value

112 return type(self)(result)

113

114 def __repr__(self):

115 return '%s(%r)' % (type(self).__name__, self.value)

116

117 In interactions between ``ArrayLike`` objects and numbers or numpy arrays,

118 the result is always another ``ArrayLike``:

119

120 >>> x = ArrayLike([1, 2, 3])

121 >>> x - 1

122 ArrayLike(array([0, 1, 2]))

123 >>> 1 - x

124 ArrayLike(array([ 0, -1, -2]))

125 >>> np.arange(3) - x

126 ArrayLike(array([-1, -1, -1]))

127 >>> x - np.arange(3)

128 ArrayLike(array([1, 1, 1]))

129

130 Note that unlike ``numpy.ndarray``, ``ArrayLike`` does not allow operations

131 with arbitrary, unrecognized types. This ensures that interactions with

132 ArrayLike preserve a well-defined casting hierarchy.

133

134 .. versionadded:: 1.13

135 """

136 # Like np.ndarray, this mixin class implements "Option 1" from the ufunc

137 # overrides NEP.

138

139 # comparisons don't have reflected and in-place versions

140 __lt__ = _binary_method(um.less, 'lt')

141 __le__ = _binary_method(um.less_equal, 'le')

142 __eq__ = _binary_method(um.equal, 'eq')

143 __ne__ = _binary_method(um.not_equal, 'ne')

144 __gt__ = _binary_method(um.greater, 'gt')

145 __ge__ = _binary_method(um.greater_equal, 'ge')

146

147 # numeric methods

148 __add__, __radd__, __iadd__ = _numeric_methods(um.add, 'add')

149 __sub__, __rsub__, __isub__ = _numeric_methods(um.subtract, 'sub')

150 __mul__, __rmul__, __imul__ = _numeric_methods(um.multiply, 'mul')

151 __matmul__, __rmatmul__, __imatmul__ = _numeric_methods(

152 um.matmul, 'matmul')

153 # Python 3 does not use __div__, __rdiv__, or __idiv__

154 __truediv__, __rtruediv__, __itruediv__ = _numeric_methods(

155 um.true_divide, 'truediv')

156 __floordiv__, __rfloordiv__, __ifloordiv__ = _numeric_methods(

157 um.floor_divide, 'floordiv')

158 __mod__, __rmod__, __imod__ = _numeric_methods(um.remainder, 'mod')

159 __divmod__ = _binary_method(um.divmod, 'divmod')

160 __rdivmod__ = _reflected_binary_method(um.divmod, 'divmod')

161 # __idivmod__ does not exist

162 # TODO: handle the optional third argument for __pow__?

163 __pow__, __rpow__, __ipow__ = _numeric_methods(um.power, 'pow')

164 __lshift__, __rlshift__, __ilshift__ = _numeric_methods(

165 um.left_shift, 'lshift')

166 __rshift__, __rrshift__, __irshift__ = _numeric_methods(

167 um.right_shift, 'rshift')

168 __and__, __rand__, __iand__ = _numeric_methods(um.bitwise_and, 'and')

169 __xor__, __rxor__, __ixor__ = _numeric_methods(um.bitwise_xor, 'xor')

170 __or__, __ror__, __ior__ = _numeric_methods(um.bitwise_or, 'or')

171

172 # unary methods

173 __neg__ = _unary_method(um.negative, 'neg')

174 __pos__ = _unary_method(um.positive, 'pos')

175 __abs__ = _unary_method(um.absolute, 'abs')

176 __invert__ = _unary_method(um.invert, 'invert')