Source code for chainmap.chainmap

from collections import MutableMapping
    from thread import get_ident
except ImportError:
        from threading import _get_ident as get_ident
    except ImportError:
        from threading import get_ident

def _recursive_repr(fillvalue='...'):
    'Decorator to make a repr function return fillvalue for a recursive call'

    def decorating_function(user_function):
        repr_running = set()

        def wrapper(self):
            key = id(self), get_ident()
            if key in repr_running:
                return fillvalue
                result = user_function(self)
            return result

        # Can't use functools.wraps() here because of bootstrap issues
        wrapper.__module__ = getattr(user_function, '__module__')
        wrapper.__doc__ = getattr(user_function, '__doc__')
        wrapper.__name__ = getattr(user_function, '__name__')
        wrapper.__annotations__ = getattr(user_function, '__annotations__', {})
        return wrapper

    return decorating_function

[docs]class ChainMap(MutableMapping): ''' A ChainMap groups multiple dicts (or other mappings) together to create a single, updateable view. The underlying mappings are stored in a list. That list is public and can accessed or updated using the *maps* attribute. There is no other state. Lookups search the underlying mappings successively until a key is found. In contrast, writes, updates, and deletions only operate on the first mapping. ''' def __init__(self, *maps): '''Initialize a ChainMap by setting *maps* to the given mappings. If no mappings are provided, a single empty dictionary is used. ''' self.maps = list(maps) or [{}] # always at least one map def __missing__(self, key): raise KeyError(key) def __getitem__(self, key): for mapping in self.maps: try: return mapping[key] # can't use 'key in mapping' with defaultdict except KeyError: pass return self.__missing__(key) # support subclasses that define __missing__ def get(self, key, default=None): return self[key] if key in self else default def __len__(self): return len(set().union(*self.maps)) # reuses stored hash values if possible def __iter__(self): return iter(set().union(*self.maps)) def __contains__(self, key): return any(key in m for m in self.maps) def __bool__(self): return any(self.maps) @_recursive_repr() def __repr__(self): return '{0.__class__.__name__}({1})'.format( self, ', '.join(map(repr, self.maps))) @classmethod def fromkeys(cls, iterable, *args): 'Create a ChainMap with a single dict created from the iterable.' return cls(dict.fromkeys(iterable, *args)) def copy(self): 'New ChainMap or subclass with a new copy of maps[0] and refs to maps[1:]' return self.__class__(self.maps[0].copy(), *self.maps[1:]) __copy__ = copy def new_child(self, m=None): # like Django's Context.push() ''' New ChainMap with a new map followed by all previous maps. If no map is provided, an empty dict is used. ''' if m is None: m = {} return self.__class__(m, *self.maps) @property def parents(self): # like Django's Context.pop() 'New ChainMap from maps[1:].' return self.__class__(*self.maps[1:]) def __setitem__(self, key, value): self.maps[0][key] = value def __delitem__(self, key): try: del self.maps[0][key] except KeyError: raise KeyError('Key not found in the first mapping: {0!r}'.format(key)) def popitem(self): 'Remove and return an item pair from maps[0]. Raise KeyError is maps[0] is empty.' try: return self.maps[0].popitem() except KeyError: raise KeyError('No keys found in the first mapping.') def pop(self, key, *args): 'Remove *key* from maps[0] and return its value. Raise KeyError if *key* not in maps[0].' try: return self.maps[0].pop(key, *args) except KeyError: raise KeyError('Key not found in the first mapping: {0!r}'.format(key)) def clear(self): 'Clear maps[0], leaving maps[1:] intact.' self.maps[0].clear()