python doctest: expected result is the same as the "got" result but the test failed

I am on a learning stage of using python as a tool for software QA.

I wrote the next simple test in order to find the letter 'a' in a text file number matrix. problem is that the test fails even though the expect equals to what i got.

Why is that? Can you tell me what am I doing wrong?

test script:

fin = open("abc.txt", "r")

arr_fin = []

for line in fin:
    arr_fin.append(line.split())

print arr_fin

for row in arr_fin:     
   arr_fin_1 = " ".join('{0:4}'.format(i or " ") for i in row) 
   print arr_fin_1



def find_letter(x, arr_fin_1):
    """
    >>> find_letter('a', arr_fin_1)
    97 
    """
    t=ord(x) #exchange to letter's ASCII value
    for i in arr_fin_1:
        if i==x:
            print t
            return;

def _test():
    import doctest
    doctest.testmod()

if __name__ == "__main__":
    _test()

error message:

Expected:
    97 
Got:
    97
**********************************************************************
1 items had failu开发者_高级运维res:
   1 of   1 in __main__.find_letter
***Test Failed*** 1 failures.

You've got an extra space after the 97 - if you remove it, your test should run fine.

This:

return;

Makes your function return None.

Did you mean return t?

Besides that, IMHO doctest tests are meant to be self-contained. This is something the user should see in your documentation and understand without context. In your example, you're using a module-local arr_fin_1 object which is completely opaque to the user. It's better to define it in the doctest before the find_letter call to provide a self-contained example.