Python老男孩 day15 函数（三） 前向引用之'函数即变量'

https://www.cnblogs.com/linhaifeng/articles/6113086.html

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六、前向引用之'函数即变量'

def foo():
    print('from foo')
    bar()

foo()

运行结果：
NameError: name 'bar' is not defined

def foo():
    print('from foo')
    bar()

def bar():
    print('from bar')
foo()

运行结果：
from foo
from bar

def foo():
    print('from foo')
    bar()

foo()

def bar():
    print('from bar')

运行结果：
NameError: name 'bar' is not defined
from foo