Python String Methods: upper, strip, replace, find

What Is a String Method? upper(), lower() and title()

A method is a tool that belongs to a value. You call it with a dot: the value, a dot, the method name and brackets, like name.upper(). Strings come with dozens of methods.

Think of it like the buttons on a TV remote. The string is the TV, and .upper() is the button you press to make it do something.

12345name = "sunny kumar"
print(name.upper())
print(name.title())
print(name.capitalize())
print("HELLO".lower())

You already used methods on lists in chapter 9, like nums.append(5). Same dot, same brackets.

The rules

• Write the brackets, even when they're empty: name.upper().
• A string method returns a new string. The original never changes, because strings are immutable.
• To keep the result, store it: name = name.upper().

Avoid: calling a method and throwing the result away

123name = "rocky"
name.upper()
print(name)

No error, but nothing changed! name.upper() made "ROCKY", and nobody stored it.

Good: store the new string

123name = "rocky"
name = name.upper()
print(name)

Common beginner doubt: "Why did list.append() change the list, but upper() doesn't change the string?" Lists can change, so their methods change them in place. Strings can't change, so their methods always hand you a new string instead.

A string method returns a new string. Store it if you want to keep it.

Remove Extra Spaces with strip()

The strip() method removes spaces from both ends of a string. Spaces in the middle stay. It also removes tabs and new lines at the ends.

Think of it like trimming the crust off a slice of bread: the edges go, the middle stays.

12345text = "   Sunny   "
print("[" + text + "]")
print("[" + text.strip() + "]")
print("[" + text.lstrip() + "]")
print("[" + text.rstrip() + "]")

The square brackets are only there so you can see the spaces.

The rules

• The middle is never touched: "Sunny Kumar".strip() keeps both spaces.
• Put characters in the brackets to strip those instead: "**hi**".strip("*") gives "hi".

Chain methods to clean up answers

In chapter 8, "Yes" with a capital Y, or with a space, didn't match "yes". Now you can fix that. Chain two methods: each one works on the result of the one before, from left to right.

12345answer = input()
if answer.strip().lower() == "yes":
    print("Great, let's start!")
else:
    print("Maybe later.")

" YES" becomes "YES" after strip(), then "yes" after lower(), and the comparison is True.

Common beginner doubt: "Should I always strip user input?" For text answers, yes: people often type a space by accident. For int(input()) you don't need to, because int() ignores spaces at the ends by itself.

strip() trims the ends, and strip().lower() makes user answers easy to compare.

Replace Text with replace()

The replace() method swaps one piece of text for another: text.replace(old, new). It returns a new string with every old changed to new.

Think of it like "Find and replace" in a word processor: type what to find, type what to put instead, and every match changes at once.

12msg = "I like cats. cats are cute."
print(msg.replace("cats", "dogs"))

Remove text

Replace something with an empty string "", and it disappears:

123phone = "98-765-43210"
print(phone.replace("-", ""))
print("Sunny  Kumar".replace("  ", " "))

The second line fixes the double space in the middle that strip() couldn't touch.

The rules

• It replaces every match, not only the first.
• It's case-sensitive: "Cats" won't match "cats".
• If nothing matches, you get the same text back. No error.
• A third value limits how many to replace: "a-b-c".replace("-", " ", 1) gives "a b-c".
• Like every string method, it returns a new string. Store it to keep it.

Avoid: the wrong capitals

12greeting = "Hello World"
print(greeting.replace("world", "Sunny"))

Nothing changed, and there's no error to warn you: "world" with a small w isn't in the text. Copy the exact capitals.

Common beginner doubt: "Can I replace several different things?" Yes, chain them: text.replace("-", "").replace(" ", "") removes the dashes, then the spaces.

text.replace(old, new) swaps every match and returns a new string.

Search a String: find(), count() and startswith()

Four methods search a string for you. find() says where a piece is, count() says how many times it appears, and startswith() and endswith() say yes or no.

Think of it like pressing Ctrl+F on a web page: the browser shows where the word is and how many matches there are.

12345email = "sunny@example.com"
print(email.find("@"))
print(email.count("m"))
print(email.endswith(".com"))
print(email.startswith("rocky"))

The rules

All of them are case-sensitive.

find() and slicing together

find() gives an index, and an index is exactly what a slice needs. Here's how to cut the name out of an email address:

1234email = "sunny@example.com"
at = email.find("@")
print(email[:at])
print(email[at + 1:])

Avoid: using -1 as an index by mistake

When find() finds nothing, it gives -1, not an error. But -1 is also a real index: the last character!

1234name = "Sunny"
pos = name.find("z")
print(pos)
print(name[pos])

No error, but a wrong answer. Check first: if pos != -1:, then use it.

Common beginner doubt: "find() or in?" Use in when you only need yes or no. Use find() when you need the position.

find() says where, count() says how many, startswith() and endswith() say yes or no.

Check Text with isdigit() and isalpha()

isdigit() gives True when every character of a string is a digit from 0 to 9. isalpha() gives True when every character is a letter. They let you check text before you use it.

Think of it like a ticket checker at a gate: the ticket is looked at first, and only a good one gets through.

The rules

• isdigit() is False for "-5" and "3.5": the minus sign and the point aren't digits.
• An empty string "" is False for both.
• isalpha() is False as soon as there's a space or a digit.
• Like startswith(), these give True or False, so they fit straight into an if.

123456print("2024".isdigit())
print("-5".isdigit())
print("3.5".isdigit())
print("".isdigit())
print("Sunny".isalpha())
print("Sunny 1".isalpha())

Avoid: int() on text that isn't a number

12age = int(input())
print(age + 1)

You met this error in chapter 7. int() can't turn "twenty" into a number, so the program crashes.

Good: check first, then convert

123456text = input()
if text.isdigit():
    age = int(text)
    print("Next year you will be", age + 1)
else:
    print("Please type a number.")

Type 20 in the Input box and run it again: now the number is used.

Common beginner doubt: "What about negative numbers and decimals?" isdigit() is perfect for whole numbers like ages and quantities. For any kind of bad input, there's a stronger tool called try and except. You'll learn it in chapter 17.

Check text with isdigit() before you turn it into an int.

Practice: Methods

Solve these to lock in what you learned in this topic. Each one runs in your browser.

1. 102.Python Program to Clean Up a Name with strip() and title()EasySolve
2. 103.Python Program to Count the Vowels in a SentenceMediumSolve
3. 104.Python Program to Check a Simple Email AddressMediumSolve