Python String Basics: Finding Substrings and Getting Length

1. Get string length and count occurrences

str1 = "我的电脑有点卡了，你的电脑卡吗？"
print(len(str1))          # 16
print(str1.count("电脑")) # 2

The length of str1 is 16 characters, and the substring "电脑" appears twice.

2. Convert string case

str2 = " i Miss you VERY much"
print(str2.upper())   # I MISS YOU VERY MUCH
print(str2.lower())   # i miss you very much
print(str2.swapcase())# I miSS TOU very MUCH
print(str2.title())   # I Miss You Very Much

These calls illustrate upper(), lower(), swapcase(), and title() transformations.

3. Find substring positions

str3 = "abcdefghijklmn123987654zxyslt"
print(str3.find("l"))        # 11
print(str3.find("o"))        # -1
print(str3.index("a"))       # 0
# print(str3.index("p")) would raise ValueError
print(str3.rfind("l"))       # 28
print(str3.rfind("q"))       # -1
print(str3.find("l", 3, 12)) # 11
print(str3.index("l", 3, 12))# 11

find()

returns the first index or -1 if not found, index() behaves similarly but raises an error when the substring is absent, and rfind() returns the last occurrence. The optional start and end arguments limit the search range.