Python String Methods

Text from the real world is messy. People type their email with extra spaces, write their name in ALL CAPS or enter a phone number with dashes. Python string methods are the built-in tools that clean up, search and reshape that text. In this lesson, you'll learn the methods you'll use every week, see how to chain them, and get a reference table to come back to.

What is a string method?

A method is a function that belongs to a value. You call it by writing the value, a dot, the method name and parentheses:

city = "paris"
print(city.upper())
print(city.title())

PARIS
Paris

Read city.upper() as "ask the string in city to give me an uppercase version". Some methods need extra information inside the parentheses, called arguments. You'll learn to write your own functions in Python functions.

Do string methods change the original string?

No. Strings are immutable (they can't be changed), as you learned in Python strings. Every method returns a new string and leaves the original alone:

name = "olivia"
name.upper()
print(name)

name = name.upper()
print(name)

olivia
OLIVIA

The second line created "OLIVIA" but threw it away. To keep the result, assign it to a variable, as the fourth line does.

Changing case: upper, lower, title, capitalize

song = "bohemian rhapsody by QUEEN"
print(song.upper())
print(song.lower())
print(song.title())
print(song.capitalize())

BOHEMIAN RHAPSODY BY QUEEN
bohemian rhapsody by queen
Bohemian Rhapsody By Queen
Bohemian rhapsody by queen

title() capitalizes the first letter of every word, while capitalize() capitalizes only the first letter of the whole string and lowercases the rest.

lower() is also the standard way to compare text without caring about case:

answer = "YES"
print(answer == "yes")
print(answer.lower() == "yes")

False
True

Removing spaces: strip, lstrip, rstrip

strip() removes whitespace (spaces, tabs and line breaks) from both ends of a string. lstrip() only cleans the left side and rstrip() only the right. Spaces in the middle are kept.

raw = "   Sam Lee   "
print("[" + raw.strip() + "]")
print("[" + raw.lstrip() + "]")
print("[" + raw.rstrip() + "]")

[Sam Lee]
[Sam Lee   ]
[   Sam Lee]

You can also tell strip() which characters to remove:

price = "$$49.99$$"
print(price.strip("$"))

49.99

Replacing text with replace()

replace(old, new) swaps every occurrence of old with new:

phone = "555-0142-889"
print(phone.replace("-", ""))

message = "I love tea. Tea is the best."
print(message.replace("tea", "coffee"))

5550142889
I love coffee. Tea is the best.

Notice that "Tea" with a capital T was not replaced. Like ==, replace() is case-sensitive.

How do you split a string in Python?

split() cuts a string into pieces and returns them as a list, a collection of values in square brackets. (You'll study lists in Python lists.) With no argument, it splits on any whitespace:

sentence = "pack   my bag now"
print(sentence.split())

line = "Lena,29,Berlin"
print(line.split(","))

['pack', 'my', 'bag', 'now']
['Lena', '29', 'Berlin']

How do you join strings in Python?

join() is the opposite of split(). You call it on the separator and pass the pieces:

words = ["red", "green", "blue"]
print(", ".join(words))
print("-".join(words))
print("".join(words))

red, green, blue
red-green-blue
redgreenblue

Searching: find, index, count

find() returns the index where some text first appears, or -1 if it isn't there. index() does the same but raises an error when the text is missing. count() tells you how many times the text appears.

email = "maya.chen@example.com"
print(email.find("@"))
print(email.find("#"))
print(email.count("."))

9
-1
2

email = "maya.chen@example.com"
print(email.index("#"))

ValueError: substring not found

Combine find() with slicing to cut a string at a character you can't predict the position of:

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

maya.chen
example.com

Checking the start and end: startswith, endswith

url = "https://shop.example.com"
file = "invoice_march.pdf"

print(url.startswith("https://"))
print(file.endswith(".pdf"))
print(file.endswith(".PDF"))

True
True
False

Checking content: isdigit, isalpha, isalnum

These methods answer yes/no questions about every character in the string and return True or False:

print("2026".isdigit())
print("12.5".isdigit())
print("Oslo".isalpha())
print("New York".isalpha())
print("player42".isalnum())

True
False
True
False
True

"12.5" fails because . isn't a digit, and "New York" fails because a space isn't a letter. isdigit() is a great check before converting input with int().

Chaining string methods

Because each method returns a new string, you can call another method on the result straight away. This is called method chaining, and Python runs it from left to right.

title = "  My Summer Trip  "
slug = title.strip().lower().replace(" ", "-")
print(slug)
print("[" + title + "]")

my-summer-trip
[  My Summer Trip  ]

That result is a slug, the readable part of a web address, like example.com/blog/my-summer-trip.

Python string methods reference table

Real-world example: cleaning a form entry and a data line

email_input = "  Sam.Rivera@Example.COM  "
clean_email = email_input.strip().lower()
print(clean_email)
print("Valid-looking?", "@" in clean_email and clean_email.endswith(".com"))

row = " Espresso ; 3.50 ; hot "
parts = row.split(";")
drink = parts[0].strip()
price = float(parts[1].strip())
print(drink, "costs", price)

sam.rivera@example.com
Valid-looking? True
Espresso costs 3.5

parts[0] picks the first piece from the list that split() returned, using the same index idea you learned for strings.

Common mistakes with string methods

1. Forgetting to save the result

color = "  blue  "
color.strip()
print(len(color))

8

The spaces are still there. Write color = color.strip() to keep the cleaned version.

2. Forgetting the parentheses

print("hello".upper)

This prints something like <built-in method upper of str object at 0x7f3a...> (the number differs on every computer). Without (), you get the method itself, not its result. Always call it: "hello".upper().

3. Calling join on the list

words = ["a", "b"]
print(words.join("-"))

AttributeError: 'list' object has no attribute 'join'

The separator comes first: "-".join(words).

4. Checking find() as if it were True or False

"cat".find("c") returns 0, which is a valid position, not "not found". Not found is -1. If you just want yes or no, use "c" in "cat".

Practice exercise

raw_name = "   aDA   lOVELACE "
name = " ".join(raw_name.split()).title()
print(name)

parts = name.split()
print(parts[0][0] + "." + parts[1][0] + ".")
print(len(name.replace(" ", "")))

Ada Lovelace
A.L.
11

What's next?

You can now clean and search text. Next, learn the modern way to build strings that mix text and values in Python f-strings.