Check if a sentence is a pangram in Python

A pangram is a sentence that uses every letter of the alphabet at least once, like "The quick brown fox jumps over the lazy dog". If you take away the letters the sentence uses from the 26 letters a to z, whatever is left is missing.

The program

import string

def missing_letters(sentence):
    used = set(sentence.lower())
    return sorted(set(string.ascii_lowercase) - used)

sentences = [
    "The quick brown fox jumps over the lazy dog",
    "Pack my box with five dozen liquor jugs",
    "Grace Hopper wrote the first compiler",
]

for sentence in sentences:
    missing = missing_letters(sentence)
    if missing:
        print(f"{sentence!r}: not a pangram, missing {''.join(missing)}")
    else:
        print(f"{sentence!r}: pangram")

'The quick brown fox jumps over the lazy dog': pangram
'Pack my box with five dozen liquor jugs': pangram
'Grace Hopper wrote the first compiler': not a pangram, missing bdjknquvxyz

How it works

• string.ascii_lowercase is the string "abcdefghijklmnopqrstuvwxyz".
• set(sentence.lower()) is the set of different characters in the sentence. Spaces and punctuation are in it too, but that does not matter, because they are never in the alphabet set.
• - between two sets is the set difference: the letters in the alphabet that are not in the sentence. An empty result means the sentence is a pangram.
• sorted() puts the missing letters in alphabetical order, because a set has no order.

Another way: a loop

Without sets, check each letter of the alphabet with in:

sentence = "Grace Hopper wrote the first compiler"
text = sentence.lower()

missing = ""
for letter in "abcdefghijklmnopqrstuvwxyz":
    if letter not in text:
        missing += letter

print("Missing:", missing)
print("Pangram" if missing == "" else "Not a pangram")

Missing: bdjknquvxyz
Not a pangram

If you only need a yes or no answer, set(string.ascii_lowercase) <= set(sentence.lower()) is True for a pangram. <= between sets means "is a subset of". See subset and superset for more about it.