Strings

A string (str) is Python’s built-in type for representing text: any sequence of characters, from a single letter to an entire document. Strings are one of the most frequently used types in Python, and understanding how they behave — especially their immutability — is essential.

Creating Strings

You can create a string with single quotes, double quotes, or triple quotes. Single and double quotes behave identically — pick whichever lets you avoid escaping an apostrophe or quotation mark inside the text.

Python

single = 'Hello, world!'
double = "Hello, world!"
mixed = "It's a sunny day"      # double quotes avoid escaping the apostrophe
also_mixed = 'She said "hi"'    # single quotes avoid escaping the double quotes

print(single == double)  # True - just different syntax for the same string type

Triple-Quoted and Multi-line Strings

Triple quotes (""" or ''') let a string span multiple lines without needing explicit newline characters, and are also used for documentation strings (docstrings).

Python

poem = """Roses are red,
Violets are blue,
Python is fun,
And so are you."""

print(poem)
# Roses are red,
# Violets are blue,
# Python is fun,
# And so are you.

Strings Are Immutable

Once a string is created, it can never be changed in place. Every operation that appears to “modify” a string — concatenation, replacement, uppercasing — actually builds and returns a brand-new string object, leaving the original untouched.

Python

text = "hello"

# text[0] = "H"     # TypeError: 'str' object does not support item assignment

new_text = "H" + text[1:]  # instead, build a new string
print(new_text)             # Hello
print(text)                 # hello -- the original is unchanged

Note

Immutability has real consequences: repeatedly “modifying” a string in a loop (e.g. `result += chunk`) creates a new string object every iteration, which can be slow for very large amounts of text. For heavy string building, `''.join(list_of_pieces)` is the idiomatic, faster alternative.

Indexing and Slicing

Since a string is a sequence of characters, you can access individual characters by index (starting at 0) or extract a sub-string with a slice. Negative indices count from the end.

Python

word = "Python"

print(word[0])     # P  -- first character
print(word[-1])    # n  -- last character
print(word[0:3])   # Pyt -- characters at index 0, 1, 2 (3 is excluded)
print(word[3:])    # hon -- from index 3 to the end
print(word[:2])    # Py  -- from the start up to (not including) index 2
print(word[::-1])  # nohtyP -- reversed, using a step of -1
print(word[::2])   # Pto  -- every second character

Concatenation and Repetition

The + operator joins strings together, and * repeats a string a given number of times. Both produce a new string.

Python

greeting = "Hello" + ", " + "world" + "!"
print(greeting)  # Hello, world!

separator = "-" * 20
print(separator)  # --------------------

border = "=" * 3 + " Title " + "=" * 3
print(border)  # === Title ===

Escape Sequences

Escape sequences let you embed special characters — newlines, tabs, quotes, backslashes — inside a normal string literal.

Escape	Meaning
\n	Newline
\t	Tab
\	Literal backslash
'	Literal single quote (inside a '...' string)
"	Literal double quote (inside a "..." string)
\r	Carriage return

Python

print("Line one\nLine two")     # newline
print("Name:\tAda")             # tab
print("C:\\Users\\ada")        # literal backslashes
print('It\'s here')             # escaped single quote

Raw Strings

Prefixing a string literal with r creates a raw string, where backslashes are treated as literal characters instead of the start of an escape sequence. This is especially useful for regular expressions and Windows-style file paths.

Python

path = r"C:\Users\ada\notes.txt"
print(path)  # C:\Users\ada\notes.txt -- backslashes stay literal

pattern = r"\d+\.\d+"  # a regex meaning "one or more digits, a dot, one or more digits"
print(pattern)

Tip

Reach for a raw string (`r"..."`) any time you are writing a regular expression or a Windows path, so you do not have to double every backslash.

String Length

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

Python

print(len("Python"))      # 6
print(len(""))            # 0
print(len("  spaced  "))  # 10 -- whitespace counts too

Strings and Their Elements

Strings can be created with single, double, or triple quotes.
Strings are immutable — no in-place modification is possible.
Indexing and slicing let you read (but never write) characters or sub-strings.
+ concatenates and * repeats, both producing new strings.
Raw strings (r"...") disable escape-sequence processing.
len() returns the character count of any string.