How to check if an object is an instance of a namedtuple?

試著忘記壹切 提交于 2019-11-27 01:34:36

问题


How do I check if an object is an instance of a Named tuple?


回答1:


Calling the function collections.namedtuple gives you a new type that's a subclass of tuple (and no other classes) with a member named _fields that's a tuple whose items are all strings. So you could check for each and every one of these things:

def isnamedtupleinstance(x):
    t = type(x)
    b = t.__bases__
    if len(b) != 1 or b[0] != tuple: return False
    f = getattr(t, '_fields', None)
    if not isinstance(f, tuple): return False
    return all(type(n)==str for n in f)

it IS possible to get a false positive from this, but only if somebody's going out of their way to make a type that looks a lot like a named tuple but isn't one;-).




回答2:


If you want to determine whether an object is an instance of a specific namedtuple, you can do this:

from collections import namedtuple

SomeThing = namedtuple('SomeThing', 'prop another_prop')
SomeOtherThing = namedtuple('SomeOtherThing', 'prop still_another_prop')

a = SomeThing(1, 2)

isinstance(a, SomeThing) # True
isinstance(a, SomeOtherThing) # False



回答3:


If you need to check before calling namedtuple specific functions on it, then just call them and catch the exception instead. That's the preferred way to do it in python.




回答4:


Improving on what Lutz posted:

def isinstance_namedtuple(x):                                                               
  return (isinstance(x, tuple) and                                                  
          isinstance(getattr(x, '__dict__', None), collections.Mapping) and         
          getattr(x, '_fields', None) is not None)                                  



回答5:


I use

isinstance(x, tuple) and isinstance(x.__dict__, collections.abc.Mapping)

which to me appears to best reflect the dictionary aspect of the nature of named tuples. It appears robust against some conceivable future changes too and might also work with many third-party namedtuple-ish classes, if such things happen to exist.



来源:https://stackoverflow.com/questions/2166818/how-to-check-if-an-object-is-an-instance-of-a-namedtuple

易学教程内所有资源均来自网络或用户发布的内容,如有违反法律规定的内容欢迎反馈
该文章没有解决你所遇到的问题?点击提问,说说你的问题,让更多的人一起探讨吧!