Tuple with missing value

Question

I have a function in python that does error checking on a string. If the function finds an error it will return a tuple with an error code and an identifier for that error. Later in the program I have the function that handles the error. It accepts the tuple into two variables.

errCode, i = check_string(s,pathType)

check_string is the function that produces the tuple. What I want it to does is return just zero if there is no error. When a zero is returned the above code seems to fail because there is nothing for the variable i.

Is there an easy way to get this to work or do I just need to have the program return a tuple of 0 and 0 if no error is found?

score 3 · Accepted Answer · answered Jul 29 '12 at 10:48

3

I would use the exception system for this.

class StringError(Exception):
    NO_E = 0
    HAS_Z = 1

def string_checker(string):
    if 'e' not in string:
        raise StringError('e not found in string', StringError.NO_E)
    if 'z' in string:
        raise StringError('z not allowed in string', StringError.HAS_Z)
    return string.upper()

s = 'testing'
try:
    ret = string_checker(s)
    print 'String was okay:', ret
except StringError as e:
    print 'String not okay with an error code of', e.args[1]

answered Jul 29 '12 at 10:48

Jon Clements

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1

Maybe I'm not getting the problem, but all this to simply check if the tuple contains one or two values? *Not* meant as a criticism, and clearly using the exception mechanism has its place (given EAFP), but seems more complex than necessary. – Levon Jul 29 '12 at 10:52
1

@Levon Returning error values is rather C-ish and not very Pythonic. Maybe I've read too much in-between the lines, but given the OP's first paragraph, my first thought was "use Exceptions" - in this case, `string_checker` returns a valid string (without using tuples and codes), otherwise raises, which can be handled where ever required... Just seems a "cleaner" design to me. – Jon Clements Jul 29 '12 at 10:58
1

@Levon You're welcome. It's also easy to "forget" to check error codes leading to something breaking later, or even worse, being a silent bug that does "who knows what" over time... – Jon Clements Jul 29 '12 at 11:07
Yes, that's a very valid point, and a definite advantage of exceptions, they won't let you forget them for sure :) and require to be handled. I guess it's a matter of when and where to use them, but I understand your reasons for this solution much better now. – Levon Jul 29 '12 at 11:11
Great. This is pretty much what I need. – Reimus Klinsman Jul 30 '12 at 00:32

Levon · Answer 2 · 2012-07-29T10:54:27.623

1

Why not simply check the length of the tuple before trying to retrieve the values?

err_tup = check_String(s, pathType)
if len(err_tup) == 2:
    errCode, i = err_tup
else: # assuming it can only be 1 otherwise
    errCode = err_tup

This would work without making any changes to the rest of your code that generates the tuple, and is semantically clear.

Based on "Simple is better than complex."

edited Jul 29 '12 at 10:54

answered Jul 29 '12 at 10:43

Levon

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score 1 · Answer 3 · answered Jul 29 '12 at 10:52

1

You could use None as the value for error

def check_string(s,pathType):
    # No error
    return (None, i)

answered Jul 29 '12 at 10:52

user1560838

11
2

score 0 · Answer 4 · answered Jul 29 '12 at 11:07

0

If you are going to return zero:

foo = func()
if not foo:
    print 'No errors'
else:
    # foo is tuple

answered Jul 29 '12 at 11:07

Burhan Khalid

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284

Tuple with missing value

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