Python String Methods

A method is a function that belongs to a value. You call it with a dot after the value: name.upper(). Strings have dozens of methods for changing case, cleaning text, searching and splitting. Because strings cannot change, every method that "changes" a string actually returns a new one; you keep it by assigning it to a variable.

Case and spaces

text = "  hello, PYTHON world  "
print(text.upper())
print(text.lower())
print(text.strip())
print(text.strip().title())
print(text.strip().capitalize())
print("[" + text.lstrip() + "]")

  HELLO, PYTHON WORLD  
  hello, python world  
hello, PYTHON world
Hello, Python World
Hello, python world
[hello, PYTHON world  ]

strip removes spaces (and new lines and tabs) at both ends; lstrip and rstrip remove them only on the left or the right. It is the first thing to do with text a user typed or a line read from a file. title starts every word with a capital letter, and capitalize only the first word.

Searching and replacing

sentence = "the cat sat on the mat"
print(sentence.replace("cat", "dog"))
print(sentence.count("the"))
print(sentence.find("sat"), sentence.find("bus"))
print(sentence.startswith("the"), sentence.endswith("mat"))

the dog sat on the mat
2
8 -1
True True

find gives the index where the text starts, or -1 when it is not there. replace changes every occurrence; give a third number, replace("a", "b", 1), to change only the first ones.

Splitting and joining

split cuts a string into a list of parts, and join glues a list of strings back together with a separator between them. Together they are the everyday tools for handling text data:

line = "Asha,21,Pune"
parts = line.split(",")
print(parts)
words = "learn python step by step".split()
print(len(words), "words")
print("-".join(words))
print(" | ".join(["a", "b", "c"]))

['Asha', '21', 'Pune']
5 words
learn-python-step-by-step
a | b | c

split() with no argument splits on any run of spaces and ignores spaces at the ends.

Checking what a string contains

Methods whose names start with is answer yes-or-no questions: "2026".isdigit() is True, "abc".isalpha() is True, "Python3".isalnum() is True and " ".isspace() is True. They are handy for checking input before you convert it.

Practice exercises

1. Ask nothing yet; just take " Asha Rao ", strip it and print it in upper case and in title case.
2. Count how many times the letter a appears in "banana bandana".
3. Split the date "21-10-2026" into day, month and year, and print them as 2026/10/21 using join.
4. Check with isdigit whether "42", "4.2" and "-42" are made only of digits.