143 lines
4.1 KiB
Python
143 lines
4.1 KiB
Python
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"""Object related utilities, including introspection, etc."""
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from functools import reduce
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__all__ = ('Bunch', 'FallbackContext', 'getitem_property', 'mro_lookup')
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class Bunch:
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"""Object that enables you to modify attributes."""
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def __init__(self, **kwargs):
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self.__dict__.update(kwargs)
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def mro_lookup(cls, attr, stop=None, monkey_patched=None):
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"""Return the first node by MRO order that defines an attribute.
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Arguments:
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cls (Any): Child class to traverse.
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attr (str): Name of attribute to find.
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stop (Set[Any]): A set of types that if reached will stop
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the search.
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monkey_patched (Sequence): Use one of the stop classes
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if the attributes module origin isn't in this list.
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Used to detect monkey patched attributes.
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Returns:
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Any: The attribute value, or :const:`None` if not found.
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"""
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stop = set() if not stop else stop
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monkey_patched = [] if not monkey_patched else monkey_patched
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for node in cls.mro():
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if node in stop:
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try:
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value = node.__dict__[attr]
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module_origin = value.__module__
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except (AttributeError, KeyError):
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pass
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else:
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if module_origin not in monkey_patched:
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return node
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return
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if attr in node.__dict__:
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return node
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class FallbackContext:
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"""Context workaround.
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The built-in ``@contextmanager`` utility does not work well
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when wrapping other contexts, as the traceback is wrong when
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the wrapped context raises.
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This solves this problem and can be used instead of ``@contextmanager``
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in this example::
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@contextmanager
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def connection_or_default_connection(connection=None):
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if connection:
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# user already has a connection, shouldn't close
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# after use
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yield connection
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else:
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# must've new connection, and also close the connection
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# after the block returns
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with create_new_connection() as connection:
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yield connection
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This wrapper can be used instead for the above like this::
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def connection_or_default_connection(connection=None):
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return FallbackContext(connection, create_new_connection)
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"""
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def __init__(self, provided, fallback, *fb_args, **fb_kwargs):
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self.provided = provided
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self.fallback = fallback
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self.fb_args = fb_args
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self.fb_kwargs = fb_kwargs
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self._context = None
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def __enter__(self):
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if self.provided is not None:
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return self.provided
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context = self._context = self.fallback(
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*self.fb_args, **self.fb_kwargs
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).__enter__()
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return context
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def __exit__(self, *exc_info):
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if self._context is not None:
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return self._context.__exit__(*exc_info)
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class getitem_property:
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"""Attribute -> dict key descriptor.
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The target object must support ``__getitem__``,
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and optionally ``__setitem__``.
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Example:
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>>> from collections import defaultdict
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>>> class Me(dict):
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... deep = defaultdict(dict)
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...
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... foo = _getitem_property('foo')
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... deep_thing = _getitem_property('deep.thing')
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>>> me = Me()
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>>> me.foo
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None
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>>> me.foo = 10
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>>> me.foo
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10
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>>> me['foo']
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10
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>>> me.deep_thing = 42
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>>> me.deep_thing
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42
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>>> me.deep
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defaultdict(<type 'dict'>, {'thing': 42})
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"""
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def __init__(self, keypath, doc=None):
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path, _, self.key = keypath.rpartition('.')
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self.path = path.split('.') if path else None
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self.__doc__ = doc
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def _path(self, obj):
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return (reduce(lambda d, k: d[k], [obj] + self.path) if self.path
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else obj)
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def __get__(self, obj, type=None):
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if obj is None:
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return type
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return self._path(obj).get(self.key)
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def __set__(self, obj, value):
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self._path(obj)[self.key] = value
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