Strings — Reference | Guide to Python

Strings (str) are immutable sequences of characters. They support a rich set of methods for searching, transforming, and formatting text.

Creating Strings

python

s1 = 'single quotes'
s2 = "double quotes"
s3 = """triple quotes
for multi-line"""
s4 = r"raw string: \n is literal"

Common Operations

python

text = "Hello, World!"

len(text)           # 13 — length
text[0]             # 'H' — indexing
text[-1]            # '!' — negative indexing
text[0:5]           # 'Hello' — slicing
text[7:]            # 'World!'
"Hello" in text     # True — membership
text * 2            # 'Hello, World!Hello, World!'

Python Playground

text = "Hello, World!"

print(f"Length: {len(text)}")
print(f"First: {text[0]}")
print(f"Last: {text[-1]}")
print(f"Slice: {text[0:5]}")
print(f"Contains 'World': {'World' in text}")

Output

Click "Run" to execute your code

Case Methods

Method	Description	Example
`upper()`	All uppercase	`"hello".upper()` → `"HELLO"`
`lower()`	All lowercase	`"HELLO".lower()` → `"hello"`
`title()`	Title case	`"hello world".title()` → `"Hello World"`
`capitalize()`	First char upper	`"hello".capitalize()` → `"Hello"`
`swapcase()`	Swap case	`"Hello".swapcase()` → `"hELLO"`
`casefold()`	Aggressive lowercase	`"Straße".casefold()` → `"strasse"`

Search Methods

Method	Description	Example
`find(sub)`	Index of first match, -1 if not found	`"hello".find("ll")` → `2`
`rfind(sub)`	Index of last match	`"hello".rfind("l")` → `3`
`index(sub)`	Like `find`, but raises `ValueError`	`"hello".index("ll")` → `2`
`count(sub)`	Count occurrences	`"hello".count("l")` → `2`
`startswith(s)`	Check prefix	`"hello".startswith("he")` → `True`
`endswith(s)`	Check suffix	`"hello".endswith("lo")` → `True`

Modification Methods

Method	Description	Example
`replace(old, new)`	Replace occurrences	`"hello".replace("l", "r")` → `"herro"`
`strip()`	Remove leading/trailing whitespace	`" hi ".strip()` → `"hi"`
`lstrip()`	Remove leading whitespace	`" hi ".lstrip()` → `"hi "`
`rstrip()`	Remove trailing whitespace	`" hi ".rstrip()` → `" hi"`
`center(w)`	Center in width	`"hi".center(10)` → `" hi "`
`ljust(w)`	Left justify	`"hi".ljust(10)` → `"hi "`
`rjust(w)`	Right justify	`"hi".rjust(10)` → `" hi"`
`zfill(w)`	Zero-pad	`"42".zfill(5)` → `"00042"`

Split and Join

python

# Splitting
"a,b,c".split(",")          # ['a', 'b', 'c']
"hello world".split()        # ['hello', 'world']
"a\nb\nc".splitlines()       # ['a', 'b', 'c']

# Joining
",".join(["a", "b", "c"])    # 'a,b,c'
" ".join(["hello", "world"]) # 'hello world'

Python Playground

# Split and join
csv = "apple,banana,cherry"
fruits = csv.split(",")
print(f"Split: {fruits}")

joined = " | ".join(fruits)
print(f"Joined: {joined}")

Output

Click "Run" to execute your code

Test Methods

Method	Description
`isalpha()`	All alphabetic?
`isdigit()`	All digits?
`isalnum()`	All alphanumeric?
`isspace()`	All whitespace?
`isupper()`	All uppercase?
`islower()`	All lowercase?
`istitle()`	Title case?

String Formatting

python

name = "Alice"
age = 30

# F-strings (recommended)
f"Name: {name}, Age: {age}"

# format() method
"Name: {}, Age: {}".format(name, age)
"Name: {n}, Age: {a}".format(n=name, a=age)

# Format specifiers
f"{3.14159:.2f}"      # '3.14'
f"{42:05d}"           # '00042'
f"{1000000:,}"        # '1,000,000'
f"{'hi':>10}"         # '        hi'
f"{'hi':<10}"         # 'hi        '
f"{'hi':^10}"         # '    hi    '