How to write python polyglot unittest for method using type function?

user_6414910 0
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I am trying to write python2 and python3 compatible code which uses type function. Both return different strings in 2 v/s 3, which I have to assert in my unit tests.

Python 3.7.4 (default, Oct 18 2019, 15:58:40)
>>> type(2)
<class 'int'>

Python 2.7.16 (default, Jul 24 2019, 16:45:12)
>>> type(2)
<type 'int'>

The intention here is to validate the exception messages raised from my function. For example,

def func(arg1):
    if not isinstance(arg1, int):
        raise TypeError('Expected type %s but got %s' % (type(int), type(arg1)))
        
    print("Function executed")
    
try:
    func('str')
except TypeError as e:
    assert e.args[0]== "Expected type <type 'type'> but got <type 'str'>"
    print("Correct exception was raised")

Assertion here passes in python2 but fails in python3.

python-2.7 python-3.x unit-testing python
2 Answers

Variations like this are the motivation for the assertRaisesRegexp function from the standard unittest module (which you should probably be using). (Note the spelling: Python 3 supports the only spelling from 2 (with the p), so that’s what you’d want here.)

user_85862270

Using type() in python for almost anything is not flexible. Instead you should use isinstance(var, type). It is almost the same in both versions of python 2.7 and 3:

isinstance(2, int)

This returns True in both versions every time.

Make sure you do not accidentally put the type in a string:

INCORRECT: 'int'

CORRECT: int

OR:

print(type(2) is int)

will output:

True

user_134761300
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