Walkthrough: Count Vowels

例题: 数元音字母

≈ 8 min · python-strings python-loops · Open in WolfCode

The textbook's canonical counter pattern (TP §8.7), applied to vowels instead of a single letter.

Python · runnable

def count_vowels(text):
    count = 0
    vowels = "aeiou"
    for char in text.lower():
        if char in vowels:
            count += 1
    return count

for text in ["banana", "Hello World", "AEIOU", "xyz", ""]:
    print(f"{text!r:>15}: {count_vowels(text)} vowels")

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The three-piece pattern

Initialize — count = 0
Traverse + condition — for char in text: if char in vowels:
Update + return — count += 1 then return count

The `in` operator on strings

Python · runnable

print("a" in "banana")       # True (single char)
print("ana" in "banana")     # True (substring)
print("z" in "banana")       # False

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Walkthrough: Count Vowels

The three-piece pattern

The in operator on strings

The `in` operator on strings