Strings and Text Processing字符串与文本处理

Study the two programs below. Both count vowels in the word "education".研究以下两个程序，均用于计算单词 "education" 中的元音字母数量。

Program A (for-each style):程序 A（for-each 风格）：

word   = "education"
vowels = "aeiou"
count  = 0
for ch in word:
    if ch in vowels:
        count += 1
print(count)

Program B (for-range style):程序 B（for-range 风格）：

word   = "education"
vowels = "aeiou"
count  = 0
for i in range(len(word)):
    if word[i] in vowels:
        count += 1
print(count)

A student normalises and analyses a messy CSV field.一名学生规范化并分析一个杂乱的 CSV 字段。

row    = "  Alice , Biology , 92 "
fields = row.split(",")
clean  = [f.strip().lower() for f in fields]
print(clean)
print(clean[0].count("l"))
print("bio" in clean[1])

A student explores two ways to reverse a string.一名学生在探索反转字符串的两种方法。

Method 1 (slice step):方法 1（切片步长）：

s    = "racecar"
rev1 = s[::-1]
print(rev1)

Method 2 (character loop):方法 2（字符循环）：

s    = "racecar"
rev2 = ""
for ch in s:
    rev2 = ch + rev2
print(rev2)

A program processes a sentence using the full text-processing pipeline.一个程序使用完整的文本处理流水线处理一个句子。

sentence = "The cat sat on the mat and the cat"
text  = sentence.lower().strip()
words = text.split()
total = len(words)
freq  = {}
for w in words:
    if w in freq:
        freq[w] += 1
    else:
        freq[w] = 1
top = max(freq, key=freq.get)
print(f"Total words: {total}")
print(f"Most frequent: '{top}' ({freq[top]} times)")
print(f"'cat' appears: {'yes' if 'cat' in words else 'no'}")