vowel.py

# re is the python regular expression module. its very powerful and worth learning.
import re
# unittest is the built in testing module. good for simple use cases like this.
from unittest import TestCase, TestLoader, TestResult

# compiling the regex pattern ahead of time, which adds significant speed
vowel_pattern = re.compile(r'[AEIOUaeiou]')

def is_vowel(char):
    # raising errors for invalid input is a good idea
    # pythonic design principle: let the thing crash early and often, and with a helpful error message
    if len(char) > 1:
        raise ValueError('char had length greater than 1')

    if vowel_pattern.match(char):
        return True

    return False

def remove_vowels(string):
    return re.sub(vowel_pattern, '', string)

class VowelTestCase(TestCase):
    def test_is_vowel(self):
        vowels = 'AEIOUaeiou'
        consonants = "BCDFGHJKLMNPQRSTVWXYZbcdfghjklmnpqrstvwxyz"
        not_letters = ";?<%&"

        # positive test 
        for letter in vowels:
            self.assertTrue(is_vowel(letter))

        # negative test 
        for letter in consonants:
            self.assertFalse(is_vowel(letter))

        # strange test
        # sometimes its a good idea to test against weird inputs that are outside of what you would normally use the function for
        # strictly speaking though only the positive and negative test are necessary
        for letter in not_letters:
            self.assertFalse(is_vowel(letter))

    def test_remove_vowels(self):
        string_with_vowels = "The quick brown fox jumped over the lazy brown dog."
        string_without_vowels = "Th qck brwn fx jmpd vr th lzy brwn dg."

        # positive test
        self.assertEqual(remove_vowels(string_with_vowels), string_without_vowels)

        # negative test
        self.assertNotEqual(remove_vowels(string_with_vowels), string_with_vowels)


# __name__ called at the module level refers to the name of the module itself, i.e. the filename
# a python file called from the command line automatically gets the name "__main__"
# this if __name__ == "__main__" construct is a common way to make a Python script executable from the shell
# e.g. user@host$: python script.py
if __name__ == "__main__":
    # this is a simple way to set up a unit test runner
    result = TestResult()
    suite = TestLoader().loadTestsFromTestCase(VowelTestCase)
    suite.run(result)
 
    # console output stuff
    print "TESTS: %d" % (result.testsRun)
    print "ERRORS: %d" % len(result.errors)
    for error in result.errors:
        print error
    print "FAILURES: %d" % len(result.failures)
    for failure in result.failures:
        print failure