Errors in Python Pangram Checker on Exercism.io

Question

I am trying to solve this problem on Exercism.io's Python track and am passing all tests except tests for mixed case and punctuation, only lower case, numbers, and underscores. There are 10 tests and I currently have four incorrect. Here's my code.

def is_pangram(sentence):
alphabet = "abcdefghijklmnopqrstuvwxyz"
if alphabet in sentence:
    return True
else:
    return False

Here is the test code:

class PangramTest(unittest.TestCase):
def test_empty_sentence(self):
    self.assertIs(is_pangram(""), False)

def test_perfect_lower_case(self):
    self.assertIs(is_pangram("abcdefghijklmnopqrstuvwxyz"), True)

def test_only_lower_case(self):
    self.assertIs(is_pangram("the quick brown fox jumps over the lazy dog"), True)

def test_missing_the_letter_x(self):
    self.assertIs(
        is_pangram("a quick movement of the enemy will jeopardize five gunboats"),
        False,
    )

def test_missing_the_letter_h(self):
    self.assertIs(is_pangram("five boxing wizards jump quickly at it"), False)

def test_with_underscores(self):
    self.assertIs(is_pangram("the_quick_brown_fox_jumps_over_the_lazy_dog"), True)

def test_with_numbers(self):
    self.assertIs(
        is_pangram("the 1 quick brown fox jumps over the 2 lazy dogs"), True
    )

def test_missing_letters_replaced_by_numbers(self):
    self.assertIs(is_pangram("7h3 qu1ck brown fox jumps ov3r 7h3 lazy dog"), False)

def test_mixed_case_and_punctuation(self):
    self.assertIs(is_pangram('"Five quacking Zephyrs jolt my wax bed."'), True)

def test_case_insensitive(self):
    self.assertIs(is_pangram("the quick brown fox jumps over with lazy FX"), False)

What am I missing? Is there any aspect of this conceptually that I haven't grasped that I should do further research into?

Note you could just `return "abcdefghijklmnopqrstuvwxyz" in sentence`, but that that's absolutely not the right logic. Try e.g. `"abc" in "cab"` to see why this might be a problem. — jonrsharpe, Dec 18 '19 at 22:37
Let me guess, you only pass the tests whose result is `False`? — Tomerikoo, Dec 18 '19 at 22:47
`"abc" in s` will return true only if the string `abc` occurs in `s` as a substring, i.e. in that exact order with no intervening characters. So it would return true for `xabcy` but false for `xacby` or `axbyc` etc. — Tom Karzes, Dec 18 '19 at 22:48

swaggy p · Accepted Answer · 2019-12-18T22:50:08.460

This:

alphabet = "abcdefghijklmnopqrstuvwxyz"
if alphabet in sentence:

is checking if that entire string, i.e., the string abcdefghijklmnopqrstuvwxyz, is in the sentence. it is not checking that each individual letter of that string is in the sentence.

As it stands, your program will only return true if the string being tested against contains the precise sequence abcdefghijklmnopqrstuvwxyz. None of your tests contain that string except the 2nd one, but since a couple of your tests are supposed to return false, those ones are passing.

A way of checking each letter looks something like this (and there are surely better/more pythonic ways, just trying to convey the concept of checking each letter instead of checking that entire big string):

def is_pangram(sentence):
    alphabet = "abcdefghijklmnopqrstuvwxyz"

    for char in alphabet: 
        if char not in sentence.lower(): 
            return False

    return True

Even more Pythonic: `return set(alphabet) <= set(sentence.lower())`. — kaya3, Dec 18 '19 at 22:51
It's equivalent to the `issubset` method: https://docs.python.org/3/library/stdtypes.html#frozenset.issubset — kaya3, Dec 18 '19 at 22:52

Errors in Python Pangram Checker on Exercism.io

1 Answers1