python - 这可能涉及 namespace ，但我无法弄清楚为什么在一个示例中找不到该名称，但在另一个示例中找到了

Question

这个问题在这里已经有了答案:





UnboundLocalError with nested function scopes

(4 个回答)


去年关闭。




所以我有两个简单的 Python 模块:
测试1.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 r
a = "alpha"
b = "beta"
d = "delta"
msg = "Hello {d} one, this is {a} {b}"
print(msg)
print(fmt(msg))

所以，基本上相同，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

第二个按我的预期做:

Hello {d} one, this is {a} {b}
Hello delta one, this is alpha beta

所以第一个不认为它知道 d名称。但是，如果我插入 print(dir(d))在 def fmt(*args): 之后立即进入 test1.py语句，现在找到 d ，然后不知道下一个名字， a :

Hello {d} one, this is {a} {b}
['__add__', '__class__', '__contains__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__getnewargs__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__iter__', '__le__', '__len__', '__lt__', '__mod__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__rmod__', '__rmul__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'capitalize', 'casefold', 'center', 'count', 'encode', 'endswith', 'expandtabs', 'find', 'format', 'format_map', 'index', 'isalnum', 'isalpha', 'isascii', 'isdecimal', 'isdigit', 'isidentifier', 'islower', 'isnumeric', 'isprintable', 'isspace', 'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'maketrans', 'partition', 'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase', 'title', 'translate', 'upper', 'zfill']
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

我相信有人明白发生了什么，但我不知所措。

Answer 1

这确实是标识符范围的问题。在您的 test1.py , 标识符 a , b和 d在函数作用域内未知 fmt ，因为它们既不是全局的(这就是让它们在您的 test2.py 中为人所知的原因)，也不是本地的。您可以使用 nonlocal 解决此问题。内部声明 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()