Python 如何检查变量是否为类对象

How to check a variable is class object or not

提问by pylover

Assume a simple class:

假设一个简单的类：

class MyClass(object):
    pass

.
.
.
m = MyClass
print type(m) # gets: <type 'classobj'>
# if m is classobj, how can i check a variable is class object?

My question is: how can i check a variable is a class object?

我的问题是：如何检查变量是否是类对象？

a simple solution:

一个简单的解决方案：

if str(type(m)) == "<type 'classobj'>":
    # do something

But i think there is at least one classic way to check that.

但我认为至少有一种经典的方法可以检查这一点。

采纳答案by abarnert

In 2.x, a class object can be be a type(new-style classes) or a classobj(classic classes). The typetype is a builtin, but the classobjtype is not. So, how do you get it? That's what the typesmodule is for.

在 2.x 中，类对象可以是 a type（新式类）或 a classobj（经典类）。该type类型是内置的，但classobj类型不是。那么，你如何得到它？这就是types模块的用途。

isinstance(MyClass, (types.TypeType, types.ClassType))

In 3.x, you don't need to worry about classic classes, so:

在 3.x 中，您无需担心经典类，因此：

isinstance(MyClass, type)

---

---

Even if you want to compare the types directly, you should never compare anyobjects by their str. Compare:

即使你想直接比较的类型，你永远不应该比任何通过他们的对象str。相比：

>>> class MyClassicClass:
...     pass
>>> str(type(MyClassicClass)) == "<type 'classobj'>"
True
>>> str("<type 'classobj'>") == "<type 'classobj'>"
True

You can almost always just compare objects directly:

您几乎总是可以直接比较对象：

>>> type(MyClassicClass) == types.ClassType
True
>>> "<type 'classobj'>" == types.ClassType
False

(And in the incredibly rare cases where you really do need to compare the string representation for some reason, you want the repr, not the str.)

（并且在非常罕见的情况下，由于某种原因您确实需要比较字符串表示形式，您需要的是repr，而不是str。）

回答by Piotr Hajduga

Is this what you're looking for?

这是你要找的吗？

>>> class A(object):
...    pass
>>> isinstance(A, type)
True

>>> isinstance("asd", type)
False

But works only for classes inherited from object.

但仅适用于从对象继承的类。

回答by kindall

A new-style class (derived explicitly from objectas in your example, or implicitly in Python 3) is not of type classobj. Only old-style classes are classobjs. So for your example class as written, you could simply check to see if MyClassis an instance of type, as all new-style classes are:

新式类（object在您的示例中显式派生自，或在 Python 3 中隐式派生）不是 type classobj。只有旧式的类是classobjs。因此，对于您编写的示例类，您可以简单地检查是否MyClass是 的实例type，因为所有新式类都是：

isinstance(MyClass, type)

Because all new-style classes are derived from objectyou can also do:

因为所有新式类都是从object你派生出来的，你也可以这样做：

issubclass(MyClass, object)

I would advise against:

我建议不要：

type(MyClass) == type

This will fail if the type of a class is not type, but a metaclass. Although there may be use cases for that, of course.

如果类的类型不是type，而是元类，这将失败。当然，尽管可能会有用例。

If you really need to see if you've got an old-style class, you can import the typesmodule and use types.ClassType, or just declare an old-style class and see if the class you're testing is of the same type:

如果您确实需要查看是否有旧式类，则可以导入types模块并使用types.ClassType，或者仅声明一个旧式类并查看您正在测试的类是否属于相同类型：

class OldStyleClass:
   pass
OldStyleClass = type(OldStyleClass)

isinstance(MyClass, OldStyleClass)

回答by Jochen Ritzel

Use inspect:

使用检查：

import inspect
print inspect.isclass(obj)

回答by sergzach

Sometimes the next is working (if you want to determine how to print the object):

有时下一个工作（如果你想确定如何打印对象）：

def is_class(o):
    return hasattr(o, '__dict__')