Class closure (Kind of a gotcha if done by accident)

class_closure.py

 """instance variables gotcha"""

class C:
    """Works like a closure because class body is interpreted at import time"""
    data = {}
    def __init__(self, input):
        self.data.update(input)


c = C({'a':'b'})
print(c.data)
# {'a': 'b'}

not_the_same_instance = C({'foo': 'bar'})
print(not_the_same_instance.data)
# {'a': 'b', 'foo': 'bar'}

print(c.data)
# {'a': 'b', 'foo': 'bar'}

class X:
    """methods are interpreted at runtime, so the mutable instance variable won't work as closure"""
    def __init__(self, input):
        self.data = {}
        self.data.update(input)

x = X({'a':'b'})
print(x.data)
# {'a': 'b'}

y = X({'foo': 'bar'})
print(y.data)
# {'foo': 'bar'}

print(x.data)
# {'a': 'b'}