为什么变量在函数调用完成后仍然存在-python

Question

I read from a book about some code like below, but it was not explained. As you can see, before I call the function, no variable exists. But after function call, var2 was popped form stack and removed from our namespace of func_a as what we expected. But, var1 still exists!!!

How to explain this phenomenon? Is var1 a special kind of variable?

def func_a():
    func_a.var1 = 1
    var2 = 2

>>> func_a.var1
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'function' object has no attribute 'var1'

>>> var2
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'var2' is not defined

>>> func_a()
>>> func_a.var1
1
>>> var2
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'var2' is not defined

Answer 1

How to explain this phenomenon? Is var1 a special kind of variable?

Yes, var1 is a special kind of variable. Or perhaps more precisely, it's not a variable at all. It's an attribute of an object (even though the object is a function). The object existed before the function call, and it continues to exist after.

In the function call you are adding an attribute to a global object rather than creating a variable in a local scope.

Answer 2

You are confusing the function namespace with the function object. Before the function is called, var1 doesn't exist. When the function is called, python creates a temporary local namespace for that one call. When the function hits var2 = 2 , var2 is created in the local function namespace. When the function hits func_a.var1 = 1 , python looks func_a up in the global namespace, finds the function object, and adds var1 to it. When the function exits, the local namespace disappears but the function object still exists and so will var1 .