expe: undefined python class

snippets/undefined.py

@@ -1,117 +1,64 @@
-# Example of an undefined singleton, usable with eval() functions to limit
-# possibility of NameError exceptions.
-#
-# Use with a namespace decorator like :
-#
-# class NoNameErrorNamespace:
-#     def __init__(self, ns):
-#         self.ns = ns
-#
-#     def __getitem__(self, name):
-#         try:
-#             return self.ns[name]
-#         except KeyError:
-#             return Undefined()
-#
-#     def __setitem__(self, name, value):
-#         self.ns[name] = value
-#
-# eval('x - 1')
+from functools import total_ordering
 
 
-class Undefined:
-    def __str__(self):
-        return 'Undefined'
+def init_undefined():
+    singleton = None
 
-    def __getattr__(self, name):
-        return self
+    @total_ordering
+    class Undefined:
+        def __new__(cls, *args, **kwargs):
+            return singleton
 
-    def __neq__(self, other):
-        return True
+        def __call__(self, *args, **kwargs):
+            return singleton
 
-    self = lambda self, *args, **kwargs: self
-    true = lambda *args: True
-    false = lambda *args: False
+        def __getattribute__(self, name):
+            return singleton
 
-    __eq__ = self
-    __lt__ = false
-    __gt__ = false
-    __le__ = false
-    __ge__ = false
+        def __add__(self, other):
+            return singleton
 
-    # Arithmetic operators
-    for op in ['__add__', '__sub__', '__mul__', '__matmul__', '__truediv__',
-               '__floordiv__', '__mod__', '__divmod__', '__pow__',
-               '__lshift__', '__rshift__', '__and__', '__xor__', '__or__']:
-        locals()[op] = self
-        locals()[op.replace('__', '__r', 1)] = self
-        locals()[op.replace('__', '__i', 1)] = self
+        def __sub__(self, other):
+            return singleton
 
-    __call__ = self
-    __getitem__ = self
-    __bool__ = false
-    __abs__ = self
-    __neg__ = self
-    __pos__ = self
-    __invert__ = self
-    __contains__ = self
-    __reversed__ = self
-    __length_hint__ = lambda: 0
-    __hash__ = lambda self: id(self)
+        def __eq__(self, other):
+            return singleton
 
-    __instance = None
-    def __new__(cls, *args, **kwargs):
-        if cls.__instance is None:
-            cls.__instance = super().__new__(cls)
-        return cls.__instance
+        def __req__(self, other):
+            return singleton
+
+        def __lt__(self, other):
+            return singleton
+
+        def __bool__(self):
+            return False
+
+        def __getitem__(self, name):
+            return singleton
+
+        def __setitem__(self, name, value):
+            pass
+
+        def __setattr__(self, name, value):
+            pass
+
+    singleton = object.__new__(Undefined)
+    return Undefined
 
 
-import operator
-import inspect
-import pytest
+Undefined = init_undefined()
 
+undefined = Undefined()
 
-def test():
-    assert Undefined().__lt__(1) is False
+assert undefined is Undefined()
 
-    assert Undefined() is Undefined()
-    assert Undefined().x is Undefined()
-    assert Undefined()['a'] is Undefined()
-    assert Undefined()() is Undefined()
-    assert Undefined().x('a', 1, x=3) is Undefined()
-    assert not Undefined()
-    assert not bool(Undefined())
-    assert (Undefined() - 1) is Undefined()
-    assert (1 - Undefined()) is Undefined()
-
-
-ops = [op for key, op in operator.__dict__.items() if callable(op) and key.startswith('__')]
-@pytest.mark.parametrize('obj', [1, '', [], (), {}, dict()], ids=['integer', 'string', 'list', 'tuple', 'set', 'dict'])
-@pytest.mark.parametrize('op', ops, ids=[op.__name__ for op in ops])
-def test_op(op, obj):
-    if isinstance(op, type):
-        pytest.skip()
-    name = op.__name__.strip('_').strip('0')
-    if name in ['index', 'concat', 'countOf', 'delitem', 'indexOf', 'setitem', 'attrgetter', 'iconcat']:
-        pytest.skip()
-    args_len = len([p for p in inspect.signature(op).parameters.values() if p.default is p.empty])
-    if args_len == 0:
-        pytest.skip('no arg')
-    result = Undefined()
-    if name in ['lt', 'gt', 'le', 'ge', 'truth', 'is', 'contains']:
-        result = False
-    if name in ['ne', 'not', 'is_not']:
-        result = True
-    if name in ['length_hint']:
-        result = 0
-    result_reversed = result
-    if name in ['imod', 'mod'] and obj == '':
-        result_reversed = ''
-    if args_len == 1:
-        assert op(Undefined()) is result, f'failed with {op}'
-    elif args_len == 2:
-        assert op(Undefined(), obj) is result, f'failed with {op}'
-        if name not in ['contains', 'getitem'] or (name == 'ctonains' and obj != '' and hasattr(obj, '__contains__')) or (name == 'getitem' and hasattr(obj, '__getitem__') and obj != '' and obj != [] and obj != () and obj != {}):
-            assert op(obj, Undefined()) is result_reversed, f'failed with reversed {op}'
-    else:
-        raise NotImplementedError(f'{op} {args_len}')
+assert Undefined() + Undefined() is Undefined()
+assert (Undefined() == 1) is Undefined()
+assert not bool(Undefined())
+assert undefined.a is undefined
+assert undefined.a.b.c is undefined
+assert undefined.a.b.c.d() is undefined
+assert undefined[undefined] is undefined
+undefined[1] = 0
+undefined.x = 1
+assert undefined.x is undefined