Python variable scope
Posted on 2013-11-13 00:07:37 +0900 in Technique
About variable scope
In python, the variable scope has four kinds:
- global
- class
- instance
- local
In those kinds, the class-based and instance-based may merge in some cases:
Every time, the instance-based is looked up, which has not been initialized, the class-based result will be returned if there is any. Once it is initialized, it will be in the field of the instance.
One example from stackoverflow:
class MyClass(object):
my_var = 10
def __init__(self):
print(self.my_var)
m1 = MyClass()
>>> 10 # class-based
MyClass.my_var = 20
print(m1.my_var)
>>> 20 # Only class-based available.
m2 = MyClass()
>>> 20 # class-based
m1.my_var = 30
print(MyClass.my_var)
>>> 20 # class-based,but the instance-based variable has been set in m1.
MyClass.my_var = 40
print(m1.my_var)
>>> 30
# The value WAS shared before m1.my_var = 30 had happened.
print(m2.my_var)
>>> 40 # m2.my_var's value is still shared Hide Comments
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