python - Strange behaviour of isinstance function

Question

I have a class named Factor in the module Factor.py (https://github.com/pgmpy/pgmpy/blob/dev/pgmpy/factors/Factor.py) and also have function named factor_product in Factor.py as:

def factor_product(*args):
    if not all(isinstance(phi, Factor) for phi in args):
            raise TypeError("Input parameters must be factors")
    return functools.reduce(lambda phi1, phi2: _bivar_factor_operation(phi1, phi2,     
                                                            operation='M'), args)

Now if I even pass instances of Factor to the function, it still throws TypeError. A few lines from the debugger with breakpoint set just above the if statement:

(Pdb) args
args = (<pgmpy.factors.Factor.Factor object at 0x7fed0faf76a0>, <pgmpy.factors.Factor.Factor object at 0x7fed0faf7da0>)

(Pdb) isinstance(args[0], Factor)
False

(Pdb) type(args[0])
<class 'pgmpy.factors.Factor.Factor'>

(Pdb) Factor
<class 'pgmpy.factors.Factor.Factor'>

Any idea why this is happening ?

Answer 1

reload是从同一个模块中获得同一个类的两个副本的好方法：一个来自重新加载之前（如果该类的任何实例仍然潜伏），另一个来自之后。

很可能您有新类型的对象，但Factor引用了旧类型，因为它是前一段时间导入的。因此，无论如何，您的对象不是Factor... 不是that的实例，这是完全正确的。 Factor

永远不要相信reload。:)

Answer 2

As isinstance如果 object 参数是 classinfo 参数或其（直接、间接或虚拟）子类的实例，则返回 true，如果您将类的实例而不是类本身传递给它，它只会返回 true ，请参阅以下示例：

>>> class A :
...  pass
... 
>>> isinstance(A,A)
False
>>> isinstance(A(),A)
True
>>> z=A()
>>> isinstance(z,A)
True