如何通过函数调用设置全局变量？

def set_global_variable():
    global global_var
    global_var = "This is a global variable"

set_global_variable()
print(global_var)  # 输出：This is a global variable

# global_var.py
global_var = "This is a global variable"

# main.py
import global_var

print(global_var.global_var)  # 输出：This is a global variable

class GlobalVariable:
    global_var = "This is a global variable"

obj = GlobalVariable()
print(obj.global_var)  # 输出：This is a global variable