导入后的for循环在Python一线式中不起作用 [英] For loop after import doesn't work in Python one-liner

问题描述

如果我使用import，并且随后出现for，则会出现invalid syntax错误.我不知道为什么会这样.

If I use import and a for follows afterwards I get an invalid syntax error. I have no idea why this happens.

> python3 -c 'import os; for a in range(1,5): print(a)'
  File "<string>", line 1
    import os; for a in range(1,5): print(a)
                 ^

删除import效果很好:

> python3 -c 'for a in range(1,5): print(a)'
1
2
3
4

或完全删除for循环:

> python3 -c 'import os; print(10)'
10

那是怎么回事?

推荐答案

这是一个错误，因为它不在Python语法中.

It's an error because it's not in the Python grammar.

如果您查看复合语句的语法规范，则说明将会看到一个语句列表(即您使用分号所做的内容)被定义为:

If you check out the syntax specification for compound statements, you'll see that a statement list (i.e. what you're making with the semicolon) is defined as:

stmt_list ::= simple_stmt (";" simple_stmt)* [";"]

和for构造不是simple_stmt，而是compound_stmt.

但是print(10)是simple_stmt，因此就很好了.

The print(10), however, is a simple_stmt and, as such, is just fine.

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