从名称实例化 Python 类
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Instantiate a Python class from a name
提问by klynch
So i have a set of classes and a string with one of the class names. How do I instantiate a class based on that string?
所以我有一组类和一个带有类名的字符串。如何根据该字符串实例化一个类？
class foo:
def __init__(self, left, right):
self.left = left
self.right = right
str = "foo"
x = Init(str, A, B)
I want x to be an instantiation of class foo.
我希望 x 是类 foo 的实例化。
采纳答案by Alex Martelli
If you know the namespace involved, you can use it directly -- for example, if all classes are in module zap, the dictionary vars(zap)is that namespace; if they're all in the current module, globals()is probably the handiest way to get that dictionary.
如果您知道所涉及的命名空间，则可以直接使用它——例如，如果所有类都在 module 中zap，则字典vars(zap)就是该命名空间；如果它们都在当前模块中，globals()则可能是获取该字典的最简便方法。
If the classes are not all in the same namespace, then building an "artificial" namespace (a dedicated dict with class names as keys and class objects as values), as @Ignacio suggests, is probably the simplest approach.
如果这些类并不都在同一个命名空间中，那么正如@Ignacio 所建议的那样，构建一个“人工”命名空间（一个专用的字典，以类名作为键和类对象作为值）可能是最简单的方法。
回答by Radagast
In your case you can use something like
在您的情况下，您可以使用类似
get_class = lambda x: globals()[x]
c = get_class("foo")
And it's even easier no get class from the module
而且更容易没有从模块中获取课程
import somemodule
getattr(somemodule, "SomeClass")
回答by Ignacio Vazquez-Abrams
classdict = {'foo': foo}
x = classdict['foo'](A, B)
回答by Mischa Arefiev
classname = "Foo"
foo = vars()[classname](Bar, 0, 4)
Or perhaps
也许
def mkinst(cls, *args, **kwargs):
try:
return globals()[cls](*args, **kwargs)
except:
raise NameError("Class %s is not defined" % cls)
x = mkinst("Foo", bar, 0, 4, disc="bust")
y = mkinst("Bar", foo, batman="robin")
Miscellaneous notes on the snippet:
关于片段的其他注释：
*argsand **kwargsare special parameters in Python, they mean ?an array of non-keyword args? and ?a dict of keyword args? accordingly.
*args并且**kwargs是 Python 中的特殊参数，它们的意思是？非关键字参数数组？和？关键字参数的字典？因此。
PEP-8 (official Python style guide) recommends using clsfor class variables.
PEP-8（官方 Python 风格指南）推荐使用clsfor 类变量。
vars()returns a dict of variables defined in the local scope.
vars()返回在本地范围内定义的变量的字典。
globals()returns a dict of variables currently present in the environment outside of local scope.
globals()返回当前存在于本地范围之外的环境中的变量的字典。
回答by roma
try this
试试这个
cls = __import__('cls_name')
and this - http://effbot.org/zone/import-confusion.htmmaybe helpful
回答by Aliaksei Kuzmin
You might consider usage of metaclass as well:
您也可以考虑使用元类：
Cls = type('foo', (), foo.__dict__)
x = Cls(A, B)
Yet it creates another similar class.
然而，它创建了另一个类似的类。
