Python isinstance（）返回datetime.date错误

Question

I am trying to compile an old 2008 code .

import datetime

if isinstance(value, datetime.date):

But I got an error:

isinstance() arg 2 must be a class, type, or tuple of classes and types Python Executable: /usr/bin/python2.6 Python Version: 2.6.5

What am I missing?

Answer 1

I suspect you have imported the wrong datetime as in:

from datetime import datetime

instead use:

import datetime

Answer 2

I am running Python 2.7 and occasionally also ran into this error. Often simply checking the type will suffice if you do not need strict instance checking.

if id(type) and type(value) in (datetime.datetime, datetime.date):
   #somecode

Answer 3

To clarify this more, you must be careful if datetime is referring to the module from import datetime or the datetime class from from datetime import datetime as both have a date attribute.

In the first case, datetime.date refers to the date class which can be used with isinstance :

import datetime
type(datetime.date)
Out[13]: type

In the second case, the datetime.date refers to the date method of the datetime class which cannot be used with isinstance and hence the error.

from datetime import datetime
type(datetime.date)
Out[15]: method_descriptor

To help avoid errors like this it's best to explictly import and use the date class using from datetime import date then use isinstance(value, date) .