Question

我想测试使用this问题答案中指定的非本地语句的示例：

def outer():
   x = 1
   def inner():
       nonlocal x
       x = 2
       print("inner:", x)
   inner()
   print("outer:", x)

但是当我尝试加载此代码时，总是会出现语法错误：

Traceback (most recent call last):


File "<stdin>", line 1, in <module>
  File "t.py", line 4
    nonlocal x
             ^
SyntaxError: invalid syntax

有人知道我在做错了什么（我得到的每个例子的语法错误都包含nonlocal）。

Answer 1

nonlocal仅适用于Python 3;它是new addition to the language。

在Python 2中，它会引发语法错误; python将nonlocal视为表达式的一部分而不是语句。

当您实际使用正确的Python版本时，此特定示例可以正常工作：

$ python3.3
Python 3.3.0 (default, Sep 29 2012, 08:16:08) 
[GCC 4.2.1 Compatible Apple Clang 3.1 (tags/Apple/clang-318.0.58)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> def outer():
...    x = 1
...    def inner():
...        nonlocal x
...        x = 2
...        print("inner:", x)
...    inner()
...    print("outer:", x)
...

Answer 2

非本地语句中列出的名称不得与本地范围中的预先存在的绑定冲突。

https://docs.python.org/3/reference/simple_stmts.html#the-nonlocal-statement

def outer():
    x = 1
    def inner():
        nonlocal x
        y = 2
        x = y
        print("inner: ", x)
    inner()
    print("outer: ", x)

def outer():
    x = 1
    def inner():
        nonlocal x
        y = 2
        x = y
        print("inner: ", x)
    inner()
    print("outer: ", x)

Python中非本地语句的语法错误

2 个答案: