我们如何在python中模拟通过引用传递？

Question

Let's say we have a function foo()

def foo():
  foo.a = 2

foo.a = 1
foo()

>> foo.a
>> 2

Is this pythonic or should I wrap the variable in mutable objects such as a list?

Eg:

a = [1]

def foo(a):
  a[0] = 2
foo()

>> a

>> 2

Answer 1

Since you "want to mutate the variable so that the changes are effected in global scope as well" use the global keyword to tell your function that the name a is a global variable. This means that any assignment to a inside of your function affects the global scope. Without the global declaration assignment to a in your function would create a new local variable.

>>> a = 0
>>> def foo():
...     global a
...     a = 1
...
>>> foo()
>>> a
1

Answer 2

Use a class (maybe a bit overkill):

class Foo:
    def __init__(self):
        self.a = 0

def bar(f):
    f.a = 2

foo = Foo()
foo.a = 1
bar(foo)
print(foo.a)