作用域 - 我想在python用exec动态执行某些语句，动态定义一个类并随后调用这个类，但是出现了问题。

Question

问题的描述 现在有一个需求，就是python中使用字符串动态定义一个类，并随后使用其中的方法。 可以运行的代码 {代码...} 直接运行这段代码是没有问题的，得到了输出&lt;__main__.MyClass instance at 0x000000000...

天蓬老师 · Answer

First of all "exec" is not a recommended method because it will bring some problems:

Some modules based on the __module__ attribute will fail, such as pickle, inspect, pydoc, etc.
Memory leak
namespace and module shutdown behavior issue

For a detailed description of these issues, please refer to: http://lucumr.pocoo.org/2011/...

If you insist on doing this, the following code can provide some reference:

tester.py

# encoding: utf-8
# tester.py

import actor

content = """
class MyClass:
    def __init__(self):
        self.name = None
        self.age = None

def do():
    return MyClass()
"""

vars = {}
code = compile(content, '', 'exec')
m_cls = actor.execute(code, vars, vars)
print m_cls.name

actor.py

# encoding: utf-8
# actor.py

def execute(content, m_globals, m_locals):
    exec(content, m_globals, m_locals)
    return m_globals['do']()

大家讲道理 · Answer

Create a class dynamically

def init(self, name):
    self.name = name

attrs = dict(name=None, age=None, __init__=init )
# type创建一个类, base object, 设置属性和__init__等
klass = type("MyClass", (object, ), attrs)

my = klass(name="Hello")

print(my)       # <__main__.MyClass object at 0x10b882290>
print(my.name)  # Hello

You may consider using exec, maybe because you are not exposed to the advanced features of python

问题的描述

可以运行的代码

不可以运行的代码