这可能涉及名称空间，但我无法弄清楚为什么在一个示例中找不到该名称，但在另一个示例中却找到了

Question

所以我有两个简单的 Python 模块：test1.py：def main():    def fmt(*args):        r = ""        for x in args:            r += eval("f'"+x+"'")        return r    a = "alpha"    b = "beta"    d = "delta"    msg = "Hello {d} one, this is {a} {b}"    print(msg)    print(fmt(msg))if __name__ == "__main__":    main()和 test2.py：def fmt(*args):    r = ""    for x in args:        r += eval("f'"+x+"'")    return ra = "alpha"b = "beta"d = "delta"msg = "Hello {d} one, this is {a} {b}"print(msg)print(fmt(msg))所以，基本上是相同的，除了第一个将代码包装在一个函数中，而第二个没有。第一个在执行时给出以下输出：Hello {d} one, this is {a} {b}Traceback (most recent call last):  File "test1.py", line 16, in <module>    main()  File "test1.py", line 13, in main    print(fmt(msg))  File "test1.py", line 6, in fmt    r += eval("f'"+x+"'")  File "<string>", line 1, in <module>NameError: name 'd' is not defined第二个如我所料：Hello {d} one, this is {a} {b}Hello delta one, this is alpha beta所以第一个认为它不知道这个d名字。但是，如果我print(dir(d))在语句之后立即插入 test1.py def fmt(*args):，现在它会找到d，然后不知道下一个名称a：Hello {d} one, this is {a} {b}Traceback (most recent call last):  File "test1.py", line 17, in <module>    main()  File "test1.py", line 14, in main    print(fmt(msg))  File "test1.py", line 7, in fmt    r += eval("f'"+x+"'")  File "<string>", line 1, in <module>NameError: name 'a' is not defined我敢肯定有人知道发生了什么，但我很茫然。

Answer 1

这确实是标识符范围的问题。在您的test1.pya中，标识符b和d在函数的范围内是未知的fmt，因为它们既不是全局的（这就是使它们在您的test2.py中已知的原因），也不是本地的。您可以使用nonlocal内部语句解决此问题fmt：

def main():

    def fmt(*args):

        nonlocal a, b, d # <----------- only added line of code

        r = ""

        for x in args:

            r += eval("f'"+x+"'")

        return r

    a = "alpha"

    b = "beta"

    d = "delta"

    msg = "Hello {d} one, this is {a} {b}"

    print(msg)

    print(fmt(msg))

if __name__ == "__main__":

    main()