class CloneDict(object):
'''
Mimics ordinary dict objects, but allows cheap shallow copy operation
>>> d = CloneDict({1: 2})
>>> d
CloneDict({1: 2})
>>> d[42] = 42
>>> d == {1: 2, 42: 42}
True
>>> d2 = d.__copy__()
>>> del d[1]
>>> d
CloneDict({42: 42})
>>> d2 == {1: 2, 42: 42}
True
'''
__slots__ = [
'base', # persistent dict
'diff', # changes relative to it
]
def __init__(self, d=None):
if isinstance(d, CloneDict):
self.base = d.base = d.base.update(d.diff)
self.diff = {}
d.diff = {}
elif d is None:
self.base = PersistentDict()
self.diff = {}
else:
self.base = PersistentDict(d)
self.diff = {}
def __copy__(self):
return CloneDict(self)
def update(self, *args, **kwargs):
self.diff.update(*args, **kwargs)
def get(self, key, default=None):
if key not in self.diff:
return self.base.get(key, default)
value = self.diff[key]
if value is NO_VALUE:
return default
else:
return value
def __getitem__(self, key):
if key not in self.diff:
return self.base[key]
value = self.diff[key]
if value is NO_VALUE:
raise KeyError()
return value
def __setitem__(self, key, value):
self.diff[key] = value
def __delitem__(self, key):
self.diff[key] = NO_VALUE
def __contains__(self, key):
if key not in self.diff:
return key in self.base
return self.diff[key] is not NO_VALUE
def keys(self):
result = []
for k, v in self.diff.items():
if v is not NO_VALUE:
result.append(k)
for k in self.base.keys():
if k not in self.diff:
result.append(k)
return result
def items(self):
result = []
for kv in self.diff.items():
k, v = kv
if v is not NO_VALUE:
result.append(kv)
for kv in self.base.items():
k, v = kv
if k not in self.diff:
result.append(kv)
return result
def __len__(self):
result = 0
for k, v in self.diff.items():
if v is not NO_VALUE:
result += 1
for k in self.base.keys():
if k not in self.diff:
result += 1
return result
def __repr__(self):
return 'CloneDict({!r})'.format(dict(self.items()))
def __eq__(self, other):
if self is other:
return True
return set(self.items()) == set(other.items())
def __ne__(self, other):
return not self.__eq__(other)
