运行包含在字符串中的 Python 代码 [英] Running Python code contained in a string

问题描述

我正在使用 pygame 和 box2d 编写游戏引擎，并且在角色构建器中，我希望能够编写将在 keydown 事件上执行的代码.

I'm writing a game engine using pygame and box2d, and in the character builder, I want to be able to write the code that will be executed on keydown events.

我的计划是在字符生成器中有一个文本编辑器，让您可以编写类似于以下内容的代码:

My plan was to have a text editor in the character builder that let you write code similar to:

if key == K_a:
    ## Move left
    pass
elif key == K_d:
    ## Move right
    pass

我将文本编辑器的内容检索为字符串，并且我希望代码在Character的这个方法中的一个方法中运行:

I will retrieve the contents of the text editor as a string, and I want the code to be run in a method in this method of Character:

def keydown(self, key):
    ## Run code from text editor

最好的方法是什么?

推荐答案

您可以使用 eval(string) 方法来做到这一点.

You can use the eval(string) method to do this.

eval(code, globals=None, locals=None)
代码只是标准的 Python 代码——这意味着它仍然需要正确缩进.

eval(code, globals=None, locals=None)
The code is just standard Python code - this means that it still needs to be properly indented.

全局变量可以定义一个自定义的 __builtins__，这对于安全目的可能很有用.

The globals can have a custom __builtins__ defined, which could be useful for security purposes.

eval("print('Hello')")

会将 hello 打印到控制台.您还可以为要使用的代码指定局部和全局变量:

Would print hello to the console. You can also specify local and global variables for the code to use:

eval("print('Hello, %s'%name)", {}, {'name':'person-b'})

安全问题

不过要小心.将执行任何用户输入.考虑:

Security Concerns

Be careful, though. Any user input will be executed. Consider:

eval("import os;os.system('sudo rm -rf /')")

有很多方法可以解决这个问题.最简单的方法是执行以下操作:

There are a number of ways around that. The easiest is to do something like:

eval("import os;...", {'os':None})

这将引发异常，而不是擦除您的硬盘驱动器.虽然您的程序是桌面程序，但如果人们重新分发脚本，这可能是一个问题，我想这是有意的.

Which will throw an exception, rather than erasing your hard drive. While your program is desktop, this could be a problem if people redistributed scripts, which I imagine is intended.

这是一个使用 eval 的例子，相当奇怪:

Here's an example of using eval rather strangely:

def hello() : print('Hello')
def world() : print('world')
CURRENT_MOOD = 'happy'

eval(get_code(), {'contrivedExample':__main__}, {'hi':hello}.update(locals()))

这在 eval 行的作用是:

What this does on the eval line is:

1. 为当前模块赋予另一个名称(它成为脚本的contrivedExample).消费者现在可以调用 contrivedExample.hello().)
2. 它将hi 定义为指向hello
3. 它将字典与执行模块中的当前全局变量列表结合起来.

1. Gives the current module another name (it becomes contrivedExample to the script). The consumer can call contrivedExample.hello() now.)
2. It defines hi as pointing to hello
3. It combined that dictionary with the list of current globals in the executing module.

失败

事实证明(感谢评论者！)您实际上需要使用 exec 语句.大哎哟.修改后的例子如下:

FAIL

It turns out (thanks commenters!) that you actually need to use the exec statement. Big oops. The revised examples are as follows:

(这看起来很熟悉！)Exec 是一个语句:
exec "code" [in scope]其中范围是局部和全局变量的字典.如果未指定，则在当前范围内执行.

(This looks familiar!) Exec is a statement:
exec "code" [in scope] Where scope is a dictionary of both local and global variables. If this is not specified, it executes in the current scope.

代码只是标准的 Python 代码 - 这意味着它仍然需要正确缩进.

The code is just standard Python code - this means that it still needs to be properly indented.

exec "print('hello')"

会将 hello 打印到控制台.您还可以为要使用的代码指定局部和全局变量:

Would print hello to the console. You can also specify local and global variables for the code to use:

eval "print('hello, '+name)" in {'name':'person-b'}

exec 安全问题

不过要小心.将执行任何用户输入.考虑:

exec Security Concerns

Be careful, though. Any user input will be executed. Consider:

exec "import os;os.system('sudo rm -rf /')"

<小时>

打印声明

正如评论者所指出的，print 是 Python 3.0 之前的所有版本中的声明.在 2.6 中，可以通过键入 from __future__ import print_statement 来更改行为.否则，使用:

---

Print Statement

As also noted by commenters, print is a statement in all versions of Python prior to 3.0. In 2.6, the behaviour can be changed by typing from __future__ import print_statement. Otherwise, use:

print "hello"

代替:

print("hello")

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