Calling freeze() on an object makes the object immutable, like const in C++. Useful if you want to make sure that a function doesn't mess with the parameters you pass to it.
Basic usage:
class Foo(object):
def __init__(self):
self.x = 1
def bar(f):
f.x += 1
f = Foo()
bar(freeze(f)) #Raises an exception
Python, 17 lines
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Copy to clipboard1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | immutable_types = set((int, str))
class Frozen(object):
def __init__(self, value):
self._value = value
def __getattribute__(self, name):
if name == '_value': return super(Frozen, self).__getattribute__(name)
v = getattr(self._value, name)
return v if v.__class__ in immutable_types else freeze(v)
def __setattr__(self, name, value):
if name == '_value': super(Frozen, self).__setattr__(name, value)
else: raise Exception("Can't modify frozen object {0}".format(self._value))
def freeze(value):
return Frozen(value)
|
nice goal; unfortunately mutables down inside "immutables" are mutable --
(Imho "freeze" / static should be in the language, for programmer sanity. "class Employee: pass" is ridiculous, namedtuple / Record close but).
oops, should be "tup = freeze(tup)" -- my mistake, delete the previous comment