Python Strings

Names, messages, passwords, product titles, tweets: most of the data people see on a screen is text. In Python, text is stored in strings. In this lesson, you'll learn how to create Python strings, combine and repeat them, measure their length, check what's inside them and compare them.

What is a string in Python?

A string is a sequence of characters. A character is a single letter, digit, space, symbol or emoji. Python's type for strings is str.

greeting = "Hello, world!"
print(greeting)
print(type(greeting))

Hello, world!
<class 'str'>

The quotes are not part of the string. They only tell Python where the text starts and ends.

How do you create a string in Python?

Put text inside quotes. Python accepts single quotes and double quotes, and they work exactly the same:

city = 'Toronto'
country = "Canada"
print(city, country)

Toronto Canada

Having two kinds of quotes is handy when your text contains one of them. Wrap the text in the other kind:

review = "It's the best pizza in town!"
quote = 'She said "see you at eight" and left.'
print(review)
print(quote)

It's the best pizza in town!
She said "see you at eight" and left.

Multi-line strings with triple quotes

Normal quotes must open and close on the same line. For text that spans several lines, use triple quotes: ''' or """. The line breaks are kept exactly as you type them.

order = """Order #1042
1 x Latte
1 x Blueberry muffin"""
print(order)

Order #1042
1 x Latte
1 x Blueberry muffin

An empty string is also a valid string: "". It has no characters at all, and it's useful as a starting value you fill in later.

How Python stores a string

Python keeps a string as a row of characters in a fixed order. Every character has a position number called an index, starting at 0. Spaces and punctuation count as characters too.

You'll use those index numbers to grab parts of a string in the next lesson, string indexing and slicing.

How do you find the length of a string?

The built-in len() function returns the number of characters in a string:

username = "pixel_panda"
print(len(username))
print(len("Hi, Sam!"))
print(len(""))

11
8
0

This is exactly how a character counter works. Here's a check for a post with a 280-character limit:

post = "Just finished my first Python program. Feeling great!"
limit = 280

print("Characters used:", len(post))
print("Characters left:", limit - len(post))
print("Too long?", len(post) > limit)

Characters used: 53
Characters left: 227
Too long? False

Joining strings with + (concatenation)

Joining strings end to end is called concatenation. Use the + operator:

first = "Maria"
last = "Lopez"
full_name = first + " " + last
print(full_name)

Maria Lopez

Python adds nothing between the pieces, so you add the space yourself. Also, + only joins a string to another string. To join a number, convert it first with str(), which you met in type conversion:

items = 3
message = "You have " + str(items) + " items in your cart"
print(message)

You have 3 items in your cart

Repeating strings with *

Multiply a string by a whole number to repeat it:

print("ha" * 3)
print("-" * 20)
print("Go! " * 2 + "Team!")

hahaha
--------------------
Go! Go! Team!

Repeating "-" or "=" is a quick way to draw a divider line in a text report.

Are Python strings immutable?

Yes. Immutable means "cannot be changed after it's created". You can't swap out one character inside an existing string:

word = "cat"
word[0] = "b"

TypeError: 'str' object does not support item assignment

Instead, you build a new string and store it in the variable. The old string is simply no longer used:

word = "cat"
word = "b" + "at"
print(word)

bat

This is why every string tool you'll learn, like +, slicing and string methods, gives you back a new string and leaves the original untouched.

Looping through the characters of a string

Because a string is a sequence, a for loop can visit its characters one by one. (You'll learn loops properly in the Python for loop; for now, just read it as "for each character in the word".)

for letter in "Wow!":
    print(letter)

W
o
w
!

How do you check if a string contains something?

The in keyword, which you met with membership operators, checks whether some text appears inside a string. not in checks the opposite.

username = "night owl"
email = "ana@example.com"

print(" " in username)
print("@" in email)
print("admin" not in username)

True
True
True

The first line catches a common sign-up rule: usernames often can't contain spaces.

Comparing strings

Use == and != to check whether two strings are exactly the same. The comparison is case-sensitive, so uppercase and lowercase letters are different characters.

password = "Sunshine42"
print(password == "Sunshine42")
print(password == "sunshine42")
print("apple" < "banana")
print("Zebra" < "apple")

True
False
True
True

< and > compare strings character by character, roughly in alphabetical order. The surprise in the last line happens because every uppercase letter comes before every lowercase letter in Python's character order. You'll see how to ignore case with .lower() in Python string methods.

Real-world example: a username checker

Let's combine what you've learned into a sign-up check that a game might run:

username = "star_gamer"

print("Username:", username)
print("Length:", len(username))
print("Long enough (5+)?", len(username) >= 5)
print("Short enough (15 max)?", len(username) <= 15)
print("No spaces?", " " not in username)

Username: star_gamer
Length: 10
Long enough (5+)? True
Short enough (15 max)? True
No spaces? True

Change the username to "al" or "the best gamer ever" and run it again to see which checks fail. Later, with if statements, you'll print a friendly error message instead of True or False.

Common mistakes with strings

1. Mismatched quotes

name = "Alex'

SyntaxError: unterminated string literal (detected at line 1)

A string must close with the same kind of quote it opened with.

2. Adding a number to a string

age = 30
print("Age: " + age)

TypeError: can only concatenate str (not "int") to str

Convert the number first: "Age: " + str(age). Or let print() do it with a comma: print("Age:", age).

3. Confusing "5" with 5

print("5" + "5")
print(5 + 5)

55
10

Text that looks like a number is still text. This matters a lot with input(), which always returns a string.

4. Trying to change one character

As you saw above, word[0] = "b" fails because strings are immutable. Build a new string and assign it instead.

Practice exercise

first_name = "Lena"
city = "Berlin"

message = first_name + " from " + city
print(message)
print(len(message))
print("*" * len(message))

Lena from Berlin
16
****************

What's next?

You can now create, join and compare whole strings. Next, learn how to grab single characters and pieces of a string with Python string indexing and slicing.