String Operations

Complete reference for Python string methods and operations. Strings in Python are immutable sequences of Unicode characters with extensive built-in functionality for text processing and manipulation.

String Creation and Basic Operations

Operation	Syntax	Example	Result	Description
String Literal	`'text'` or `"text"`	`s = "Hello"`	`"Hello"`	Create string with quotes
Multi-line String	`"""text"""`	`s = """Line 1\nLine 2"""`	Multi-line	Create multi-line string
Raw String	`r'text'`	`r'C:\path\file'`	`'C:\\path\\file'`	Ignore escape sequences
f-String	`f'text {var}'`	`f'Hello {name}'`	`'Hello John'`	Formatted string literal
Concatenation	`str1 + str2`	`"Hello" + " World"`	`"Hello World"`	Join strings together
Repetition	`str * n`	`"Ha" * 3`	`"HaHaHa"`	Repeat string n times
Membership	`substr in str`	`"ell" in "Hello"`	`True`	Check if substring exists
Length	`len(str)`	`len("Hello")`	`5`	Get string length
Indexing	`str[i]`	`"Hello"[1]`	`'e'`	Access character at index
Slicing	`str[start:end]`	`"Hello"[1:4]`	`'ell'`	Extract substring

Case Conversion Methods

Method	Purpose	Example	Result	Description
upper()	Convert to uppercase	`"hello".upper()`	`"HELLO"`	All characters to uppercase
lower()	Convert to lowercase	`"HELLO".lower()`	`"hello"`	All characters to lowercase
capitalize()	Capitalize first letter	`"hello world".capitalize()`	`"Hello world"`	First character uppercase, rest lowercase
title()	Title case	`"hello world".title()`	`"Hello World"`	First letter of each word uppercase
swapcase()	Swap case	`"Hello World".swapcase()`	`"hELLO wORLD"`	Uppercase to lowercase and vice versa
casefold()	Aggressive lowercase	`"HELLO".casefold()`	`"hello"`	More aggressive than lower()

Text Searching and Testing Methods

Method	Purpose	Example	Result	Description
find()	Find substring index	`"hello".find("ll")`	`2`	Returns index or -1 if not found
rfind()	Find from right	`"hello".rfind("l")`	`3`	Find last occurrence
index()	Find with exception	`"hello".index("ll")`	`2`	Like find() but raises ValueError if not found
rindex()	Index from right	`"hello".rindex("l")`	`3`	Like rfind() but raises ValueError
count()	Count occurrences	`"hello".count("l")`	`2`	Count non-overlapping occurrences
startswith()	Check prefix	`"hello".startswith("he")`	`True`	Check if string starts with substring
endswith()	Check suffix	`"hello".endswith("lo")`	`True`	Check if string ends with substring

Character Testing Methods

Method	Purpose	Example	Result	Description
isalpha()	All alphabetic	`"hello".isalpha()`	`True`	All characters are letters
isdigit()	All digits	`"123".isdigit()`	`True`	All characters are digits
isalnum()	Alphanumeric	`"hello123".isalnum()`	`True`	All characters are letters or digits
isspace()	All whitespace	`" ".isspace()`	`True`	All characters are whitespace
islower()	All lowercase	`"hello".islower()`	`True`	All cased characters are lowercase
isupper()	All uppercase	`"HELLO".isupper()`	`True`	All cased characters are uppercase
istitle()	Title case	`"Hello World".istitle()`	`True`	String is in title case
isdecimal()	Decimal characters	`"123".isdecimal()`	`True`	All characters are decimal
isnumeric()	Numeric characters	`"123".isnumeric()`	`True`	All characters are numeric
isascii()	ASCII characters	`"hello".isascii()`	`True`	All characters are ASCII
isprintable()	Printable characters	`"hello".isprintable()`	`True`	All characters are printable
isidentifier()	Valid identifier	`"hello_world".isidentifier()`	`True`	Valid Python identifier

String Modification Methods

Method	Purpose	Example	Result	Description
strip()	Remove whitespace	`" hello ".strip()`	`"hello"`	Remove leading/trailing whitespace
lstrip()	Remove left whitespace	`" hello ".lstrip()`	`"hello "`	Remove leading whitespace
rstrip()	Remove right whitespace	`" hello ".rstrip()`	`" hello"`	Remove trailing whitespace
replace()	Replace substring	`"hello".replace("l", "x")`	`"hexxo"`	Replace occurrences of substring
removeprefix()	Remove prefix	`"hello".removeprefix("he")`	`"llo"`	Remove prefix if present (Python 3.9+)
removesuffix()	Remove suffix	`"hello".removesuffix("lo")`	`"hel"`	Remove suffix if present (Python 3.9+)

String Splitting and Joining Methods

Method	Purpose	Example	Result	Description
split()	Split string	`"a,b,c".split(",")`	`['a', 'b', 'c']`	Split by delimiter into list
rsplit()	Split from right	`"a.b.c".rsplit(".", 1)`	`['a.b', 'c']`	Split from right with max splits
splitlines()	Split by lines	`"a\nb\nc".splitlines()`	`['a', 'b', 'c']`	Split by line breaks
partition()	Partition string	`"a-b-c".partition("-")`	`('a', '-', 'b-c')`	Split into 3 parts at first separator
rpartition()	Partition from right	`"a-b-c".rpartition("-")`	`('a-b', '-', 'c')`	Split into 3 parts at last separator
join()	Join sequence	`",".join(['a', 'b', 'c'])`	`"a,b,c"`	Join sequence elements with string

String Alignment and Padding Methods

Method	Purpose	Example	Result	Description
center()	Center align	`"hello".center(10)`	`" hello "`	Center string in given width
ljust()	Left align	`"hello".ljust(10)`	`"hello "`	Left-align string in given width
rjust()	Right align	`"hello".rjust(10)`	`" hello"`	Right-align string in given width
zfill()	Zero padding	`"42".zfill(5)`	`"00042"`	Pad with zeros on the left
expandtabs()	Expand tabs	`"a\tb".expandtabs(4)`	`"a b"`	Replace tabs with spaces

String Encoding and Decoding Methods

Method	Purpose	Example	Result	Description
encode()	Encode to bytes	`"hello".encode("utf-8")`	`b'hello'`	Encode string to bytes
decode()	Decode from bytes	`b'hello'.decode("utf-8")`	`"hello"`	Decode bytes to string

String Formatting Methods

Method	Purpose	Example	Result	Description
format()	Format string	`"Hello {}".format("World")`	`"Hello World"`	Insert values into string
format_map()	Format with mapping	`"Hello {name}".format_map({'name': 'World'})`	`"Hello World"`	Format using dictionary

Advanced String Operations

String Formatting Techniques

Technique	Syntax	Example	Result	Description
% Formatting	`"format" % values`	`"Hello %s" % "World"`	`"Hello World"`	Old-style formatting
str.format()	`"{}".format(value)`	`"Hello {}".format("World")`	`"Hello World"`	New-style formatting
f-strings	`f"text {variable}"`	`f"Hello {name}"`	`"Hello World"`	Modern formatting (Python 3.6+)

Format Specifiers

Specifier	Purpose	Example	Result	Description
{:d}	Integer	`f"{42:d}"`	`"42"`	Decimal integer
{:f}	Float	`f"{3.14159:.2f}"`	`"3.14"`	Fixed-point number
{:e}	Scientific	`f"{1000:e}"`	`"1.000000e+03"`	Scientific notation
{:g}	General	`f"{1000:g}"`	`"1000"`	General format
{:s}	String	`f"{'hello':s}"`	`"hello"`	String format
{:x}	Hexadecimal	`f"{255:x}"`	`"ff"`	Lowercase hex
{:X}	Hexadecimal	`f"{255:X}"`	`"FF"`	Uppercase hex
{:o}	Octal	`f"{8:o}"`	`"10"`	Octal format
{:b}	Binary	`f"{5:b}"`	`"101"`	Binary format
{:%}	Percentage	`f"{0.25:%}"`	`"25.000000%"`	Percentage format

Alignment and Padding in Format Strings

Format	Purpose	Example	Result	Description
{:<10}	Left align	`f"{'hello':<10}"`	`"hello "`	Left-align in 10 characters
{:>10}	Right align	`f"{'hello':>10}"`	`" hello"`	Right-align in 10 characters
{:^10}	Center align	`f"{'hello':^10}"`	`" hello "`	Center-align in 10 characters
{:0>5}	Zero padding	`f"{42:0>5}"`	`"00042"`	Pad with zeros
*{:^10}**	Custom padding	`f"{'hello':*^10}"`	`"hello*"`	Pad with custom character

Common String Operations Examples

Text Processing

# Clean and normalize text
text = "  Hello, World!  "
cleaned = text.strip().lower().replace(",", "")
print(cleaned)  # "hello world!"

# Extract file extension
filename = "document.pdf"
name, ext = filename.rsplit(".", 1)
print(f"Name: {name}, Extension: {ext}")

Data Validation

# Validate input
def is_valid_email(email):
    return "@" in email and "." in email.split("@")[-1]

# Test validation
print(is_valid_email("user@example.com"))  # True
print(is_valid_email("invalid.email"))     # False

String Building

# Efficient string building
parts = ["Hello", "beautiful", "world"]
result = " ".join(parts)
print(result)  # "Hello beautiful world"

# Template formatting
template = "Hello {name}, you have {count} messages"
message = template.format(name="Alice", count=5)
print(message)

Text Analysis

# Word frequency
text = "hello world hello python world"
words = text.split()
word_count = {word: words.count(word) for word in set(words)}
print(word_count)  # {'hello': 2, 'world': 2, 'python': 1}

# Extract numbers from text
import re
text = "The price is $25.99 and tax is $3.50"
prices = [float(match) for match in re.findall(r'\d+\.\d+', text)]
print(prices)  # [25.99, 3.5]

Performance Tips

Use join() for multiple concatenations: "".join(parts) is faster than repeated +
Use f-strings for formatting: Generally fastest formatting method
Use str methods instead of regex: Built-in methods are often faster for simple operations
Cache compiled regex patterns: If using regex repeatedly
Use string constants: For repeated string literals
Consider str.translate(): For character replacement operations

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String Operations

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