Detect Pangram

DESCRIPTION:

A pangram is a sentence that contains every single letter of the alphabet at least once. For example, the sentence "The quick brown fox jumps over the lazy dog" is a pangram, because it uses the letters A-Z at least once (case is irrelevant).

Given a string, detect whether or not it is a pangram. Return True if it is, False if not. Ignore numbers and punctuation.

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def is_pangram(s):
    s=s.lower()
    for i in range(26):
        if chr(i+97) not in s:
            return False
    return True