Strings

Introduction

Almost every program deals with text in some form — names, messages, file paths, sentences, or entire documents. In Python, text is represented using a data type called a string. You already used strings briefly in earlier lessons, but now it is time to understand exactly how they work under the hood.

In this lesson you will learn how to create strings, why they cannot be changed once created, and how to pick out individual characters or entire chunks of text using indexing and slicing.

What is a String?

A string is a sequence of characters — letters, numbers, symbols, or spaces — wrapped in quotes. In Python, the type name for a string is str.

message = "Hello, Python!"
print(message)
print(type(message))

Hello, Python!
<class 'str'>

Because a string is a sequence, Python lets you loop over it, measure its length, and access individual characters by position — just like you would with a list of items.

Creating Strings

Python gives you three ways to wrap text: single quotes, double quotes, and triple quotes. All three create the same str type — the choice mostly comes down to convenience and style.

single = 'Learning Python'
double = "Learning Python"
contains_apostrophe = "It's a sunny day"
contains_quotes = 'She said "hello"'

print(single)
print(double)
print(contains_apostrophe)
print(contains_quotes)

Learning Python
Learning Python
It's a sunny day
She said "hello"

Strings Are Immutable

Once a string is created, it cannot be changed in place. This property is called immutability. If you try to modify a single character of a string directly, Python raises an error.

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

Traceback (most recent call last):
  ...
TypeError: 'str' object does not support item assignment

Instead of modifying a string, you create a brand-new string with the changes you want. The original string is left untouched.

word = "cat"
word = "b" + word[1:]
print(word)

bat

Indexing

Every character in a string has a position, called an index. Python indexing starts at 0, not 1, so the first character is at index 0, the second at index 1, and so on.

name = "Python"

print(name[0])
print(name[1])
print(name[5])

P
y
n

Python also supports negative indexing, which counts backward from the end of the string. The last character is at index -1, the second-to-last at -2, and so on. This is handy when you do not know (or do not want to calculate) the exact length of a string.

name = "Python"

print(name[-1])
print(name[-2])

n
o

Slicing

While indexing grabs a single character, slicing grabs a whole chunk of a string using the syntax string[start:stop:step]. The start index is included, and the stop index is excluded.

word = "Programming"

print(word[0:6])
print(word[:4])
print(word[4:])
print(word[:])

Progra
Prog
ramming
Programming

You can also slice with negative indices, and you can add a step value to skip characters — for example, a step of 2 takes every second character, and a step of -1 reverses the string.

word = "Programming"

print(word[-3:])
print(word[::2])
print(word[::-1])

ing
Pormig
gnimmargorP

Concatenation and Repetition

You can join strings together using the + operator, called concatenation. You can also repeat a string multiple times using the * operator.

first = "Hello"
second = "World"

full = first + second
spaced = first + " " + second
print(full)
print(spaced)

HelloWorld
Hello World

border = "-" * 20
print(border)
print("ha" * 3)

--------------------
haha ha

Escape Sequences

Sometimes you need to include characters in a string that would otherwise confuse Python, like a quote mark inside a quoted string, or a special character like a newline or tab. Escape sequences use a backslash to represent these characters.

print("Line one\nLine two")
print("Name:\tAlex")
print('It\'s a great day')
print("File path: C:\\Users\\Alex")

Line one
Line two
Name:	Alex
It's a great day
File path: C:\Users\Alex

Multi-line Strings

Triple-quoted strings let you write text that spans several lines without needing \n escape sequences. Every line break you type becomes part of the string.

message = """Dear Student,
Welcome to the Python course.
We are glad you are here.
"""

print(message)

Dear Student,
Welcome to the Python course.
We are glad you are here.

Checking Membership with in

The in keyword lets you check whether one string appears inside another, returning True or False. This is often used inside if statements, which you will study soon.

sentence = "Python is fun to learn"

print("fun" in sentence)
print("Java" in sentence)
print("Java" not in sentence)

True
False
True

A Sneak Peek at String Methods

Beyond indexing and slicing, strings come with a large collection of built-in methods for tasks like converting case, removing extra spaces, splitting text apart, and searching for substrings. You have already seen a hint of this with functions like len(). The next lesson, String Methods, is dedicated entirely to exploring these tools in depth, so we will not cover them here.

text = "hello python"
print(len(text))

12

Common Mistakes

Best Practices

Frequently Asked Questions

Key Takeaways

Summary

Strings are one of the most frequently used data types in Python. You now know how to create them, why they cannot be modified in place, and how to extract exactly the piece of text you need using indexing and slicing.

In the next lesson, you will build on this foundation by exploring the many built-in methods Python provides for working with strings.