再来个加强版

def fun():
    global a
    a=2
def fun1():
    a=3
if __name__=='__main__':
    global a
    a=1
    print(a)
    fun()
    print(a)
    fun1()
    print(a)
    

结果：

=============== RESTART: H:\mod_spid\test4.py ==============
1
2
2
>>> 

def fun():
    global a
    a=2
def fun1():
    global a
    a=3
if __name__=='__main__':
    global a
    a=1
    print(a)
    fun()
    print(a)
    fun1()
    print(a)
    

结果：

=============== RESTART: H:\mod_spid\test4.py ==============
1
2
3
>>> 

def fun():
    global a
    a=2
def fun1():
    global a
    a=3
def fun3():
    a=4
    fun4()
def fun4():
    a=5
if __name__=='__main__':
    global a
    a=1
    print(a)
    fun()
    print(a)
    fun1()
    print(a)
    fun3()
    print(a)
    

结果：

=============== RESTART: H:\mod_spid\test4.py ==============
1
2
3
3
>>> 

最后一个：

def fun():
    global a
    a=2
def fun1():
    global a
    a=3
def fun3():
    global a
    a=4
    fun4()
def fun4():
    a=5
if __name__=='__main__':
    global a
    a=1
    print(a)
    fun()
    print(a)
    fun1()
    print(a)
    fun3()
    print(a)
    

结果：

=============== RESTART: H:\mod_spid\test4.py ==============
1
2
3
4
>>> 

结论：

Python里面，默认局部变量优先，不声明为global，都一律视为局部变量。