exec: SyntaxError: 'return' 外部函数 [英] exec: SyntaxError: 'return' outside function

问题描述

我将代码片段存储在 Postgres 数据库中.当我需要代码时，我会在数据库中找到它并使用 exec() 函数.代码片段是 extract 函数的主体.

I'm storing code snippets inside the Postgres DB. When I need the code, I find it inside the DB and use exec() function. The code snippet is a body of extract function.

不幸的是它返回SyntaxError: 'return' external function

方法

def extract(self,response):
    exec(self.custom_code)

代码片段 (repr(code_snippet))

Code snippet (repr(code_snippet))

u"return response.xpath('/text()')"

我想它应该像这样:

def extract(self,response):
    return response.xpath('/text()')

我该怎么办?这只是一行代码片段，我需要执行多行代码片段.

What I should do? This is just one line snippet and I need to execute multiline snippets.

我将 Django 与 PostgreSQL 一起使用，我意识到它会在行首删除空格 - 缩进.不知道是不是跟问题有关系.

I'm using Django with PostgreSQL and I realised that it strips spaces at the beginning of the line - indentation. I don't know if it has to do something with the problem.

尝试使用 eval 而不是 exec.现在它提出:

Tried eval instead of exec. Now it raises:

  File "/home/milano/PycharmProjects/Stilio_project/stilio/engine/models.py", line 107, in extract
    eval(self.custom_code)
  File "<string>", line 1
    return response.xpath('/text()')
         ^
SyntaxError: invalid syntax

推荐答案

Per exec 文档:

Per the exec docs:

请注意，即使在传递给 exec 的代码上下文中，也不能在函数定义之外使用 return 和 yield 语句声明.

Be aware that the return and yield statements may not be used outside of function definitions even within the context of code passed to the exec statement.

所以 exec 是明确禁止的.并且该措辞是全球性的，并非特定于 exec；在检查时，在 'single' 模式下使用代码 compile-ed 的 eval 有相同的错误；您不能像这样动态插入 return 语句.

So exec is explicitly off-limits. And that wording is global, not specific to exec; on checking, while eval using code compile-ed in 'single' mode has the same error; you can't dynamically insert return statements like this.

如果您绝对必须允许执行任意代码，我强烈建议将其限制为表达式，而不是语句，并隐式返回所述表达式的结果.因此，不是存储 u"return response.xpath('/text()')"，而是存储 u"response.xpath('/text()')"code>，并且您执行动态调用的代码将更改为:

If you absolutely must allow executing arbitrary code, I strongly recommend limiting it to expressions, not statements, and implicitly returning the result of said expressions. So instead of storing u"return response.xpath('/text()')", you'd store u"response.xpath('/text()')", and your code that performs dynamic invocation would change to:

def extract(self,response):
    return eval(self.custom_code)

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