String Methods

In the last lesson you learned to build strings and pick out parts of them. Python also gives every string a set of built-in tools for changing case, cleaning up spaces, finding and replacing text, and more. These tools are called methods.

What is a method?

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

text = "hello"
print(text.upper())

Output

Read text.upper() as "the upper-case version of text".

String methods never change the original string. They give you back a new string, which you can print or store in a variable:

text = "hello"
shout = text.upper()

print(shout)
print(text)   # still lower case

Output

Changing case

text = "learn Python today"

print(text.upper())
print(text.lower())
print(text.title())
print(text.capitalize())

Output

lower() is especially useful for comparing text that people type, because "Yes", "YES" and "yes" all become "yes".

Cleaning up spaces with strip()

strip() removes spaces from both ends of a string, but not from the middle. It's very useful for cleaning up what people type:

messy = "   hello there   "

print("[" + messy + "]")
print("[" + messy.strip() + "]")

Output

The square brackets are just there so you can see where the spaces start and end.

Going deeper: lstrip() and rstrip() optional

lstrip() removes spaces from the left end only, and rstrip() from the right end only. strip() also removes new lines and tabs, which is handy when reading lines from a file later on.

messy = "   hello there   "

print("[" + messy.lstrip() + "]")
print("[" + messy.rstrip() + "]")

Output

Chaining methods

Because each method gives back a new string, you can call another method straight away. Python works from left to right:

name = "   ADA lovelace  "
print(name.strip().title())

Output

First strip() removes the spaces, then title() capitalises each word.

Finding and replacing

sentence = "I like cats. Cats are great."

print(sentence.replace("cats", "dogs"))
print(sentence.count("a"))
print(sentence.startswith("I"))
print(sentence.endswith("!"))

Output

Notice that replace("cats", "dogs") didn't change Cats with a capital C. Methods are case-sensitive.

find() tells you the index where some text starts, or -1 if it isn't there:

sentence = "I like cats. Cats are great."

print(sentence.find("are"))
print(sentence.find("birds"))

Output

Checking for text with in

The in operator asks "does this text appear inside that text?" and answers True or False:

email = "[email protected]"

print("@" in email)
print("gmail" in email)

Output

You'll use True and False answers like this a lot once you learn if statements.

Splitting and joining

split() breaks a string into pieces. It gives you a list, a collection of values in square brackets. Lists get a whole lesson in Part 2; for now, just know that you can pick items from a list by index, exactly like characters in a string:

sentence = "the quick brown fox"
words = sentence.split()

print(words)
print(words[0])
print(words[-1])

Output

With no argument, split() splits on spaces. Give it a character to split somewhere else:

csv_line = "apple,banana,cherry"
print(csv_line.split(","))

Output

join() does the opposite: it glues pieces back together with a separator in between:

words = ["the", "quick", "brown", "fox"]
print("-".join(words))
print(" ".join(words))

Output

Methods inside f-strings

You can call methods inside the braces of an f-string:

name = "ada"
print(f"Hello, {name.title()}! Your name has {len(name)} letters.")

Output

Exercises

Exercise 1: Clean up a username

Users often type extra spaces and random capitals. Clean up the username so it prints ada_lovelace.

username = "   Ada_LoveLace  "

Output

Exercise 2: Fix the typo

The word Pyton is misspelled twice. Use a method to print the sentence with both fixed: I love Python. Python is fun!

sentence = "I love Pyton. Pyton is fun!"

Output

Exercise 3: Make it loud

Remove the extra spaces, turn the message into capitals and add an exclamation mark, so it prints HELLO WORLD!

message = "   hello world   "

Output

Exercise 4: Email parts

Split the email address into the username and the domain, and print them as Username: ada and Domain: example.com.

email = "[email protected]"

Output

String methods at a glance

A quick reference for later, including some useful methods this lesson didn't cover. Remember: every method gives back a new value and leaves the original string unchanged. Results are shown with quotes, so you can see exactly where each string starts and ends.

Changing case

Method	What it does	Example	Result
`upper()`	All capitals	`"Hello".upper()`	`'HELLO'`
`lower()`	All lower case	`"Hello".lower()`	`'hello'`
`title()`	Capital at the start of each word	`"ada lovelace".title()`	`'Ada Lovelace'`
`capitalize()`	Capital first letter, the rest lower case	`"hELLO there".capitalize()`	`'Hello there'`
`swapcase()`	Swaps capitals and lower case	`"Hello".swapcase()`	`'hELLO'`

Cleaning up and replacing

Method	What it does	Example	Result
`strip()`	Removes spaces (and new lines) from both ends	`" hi ".strip()`	`'hi'`
`lstrip()`, `rstrip()`	Removes them from the left or right end only	`" hi ".rstrip()`	`' hi'`
`strip(chars)`	Removes the given characters from both ends	`"--hi--".strip("-")`	`'hi'`
`replace(old, new)`	Swaps every `old` for `new`	`"a-b-c".replace("-", "+")`	`'a+b+c'`
`removeprefix(text)`	Removes `text` from the start, if it's there	`"Mr Smith".removeprefix("Mr ")`	`'Smith'`
`removesuffix(text)`	Removes `text` from the end, if it's there	`"photo.jpg".removesuffix(".jpg")`	`'photo'`

Finding and counting

Method	What it does	Example	Result
`find(text)`	Position of the first match, or `-1` if not found	`"banana".find("an")`	`1`
`rfind(text)`	Position of the last match, or `-1`	`"banana".rfind("an")`	`3`
`index(text)`	Like `find()`, but raises `ValueError` if not found	`"banana".index("n")`	`2`
`count(text)`	How many times `text` appears	`"banana".count("a")`	`3`
`startswith(text)`	Does the string start with `text`?	`"photo.jpg".startswith("ph")`	`True`
`endswith(text)`	Does the string end with `text`?	`"photo.jpg".endswith(".png")`	`False`

Checking what's inside

Method	What it does	Example	Result
`isdigit()`	Only digits? Great for checking typed numbers	`"2024".isdigit()`	`True`
`isalpha()`	Only letters?	`"abc1".isalpha()`	`False`
`isalnum()`	Only letters and digits?	`"abc1".isalnum()`	`True`
`isspace()`	Only spaces, tabs or new lines?	`" ".isspace()`	`True`
`isupper()`, `islower()`	All capitals, or all lower case?	`"HELLO".isupper()`	`True`

Splitting and joining

Method	What it does	Example	Result
`split()`	Splits on spaces into a list of words	`"a b c".split()`	`['a', 'b', 'c']`
`split(sep)`	Splits on `sep`	`"a,b,c".split(",")`	`['a', 'b', 'c']`
`split(sep, n)`	Splits at most `n` times	`"a,b,c".split(",", 1)`	`['a', 'b,c']`
`splitlines()`	Splits into lines	`"one\ntwo".splitlines()`	`['one', 'two']`
`partition(sep)`	Splits at the first `sep` into three parts	`"key=value".partition("=")`	`('key', '=', 'value')`
`sep.join(items)`	Glues items together with `sep` between them	`"-".join(["a", "b", "c"])`	`'a-b-c'`

Lining up text

Method	What it does	Example	Result
`center(width)`	Centres the text in `width` characters	`"hi".center(6)`	`' hi '`
`ljust(width)`	Pads on the right to `width` characters	`"hi".ljust(5)`	`'hi '`
`rjust(width)`	Pads on the left to `width` characters	`"hi".rjust(5)`	`' hi'`
`zfill(width)`	Pads a number with zeros on the left	`"42".zfill(5)`	`'00042'`

Summary

A method is a function that belongs to a value: text.upper().
String methods give back a new string. The original never changes.
upper(), lower() and title() change case. strip() removes spaces from the ends.
replace() swaps text, count() counts it, and find() gives its position (or -1).
"x" in text checks whether some text appears in a string.
split() breaks a string into a list of pieces, and "-".join(pieces) glues them back together.