Python String Methods – LivingWithCode

Python offers a wide range of built-in methods for string manipulation.

It is important to note that strings in Python are immutable, meaning they cannot be changed once created. As a result, string methods return a new, modified string instead of altering the original.

I have classified string methods into 5 categories based on their functionality. Click on any method to learn more about it.

(1) Case Conversion Methods

Method	Description	Example
`lower()`	Converts to lowercase	`"HELLO".lower()` → `"hello"`
`upper()`	Converts to uppercase	`"hello".upper()` → `"HELLO"`
`title()`	Capitalizes the first letter of each word	`"hello world".title()` → `"Hello World"`
`capitalize()`	Capitalizes the first character, lowercases the rest	`"hello WORLD".capitalize()` → `"Hello world"`
`casefold()`	Converts to lowercase more aggressively	`"Straße".casefold()` → `"strasse"`
`swapcase()`	Swaps case of each character	`"Hello".swapcase()` → `"hELLO"`

(2) Search and Find Methods

Method	Description	Example
`find()`	Returns the index of the first occurrence of the substring if found, else returns `-1`	`"hello".find("e")` → `1`
`rfind()`	Returns the index of the last occurrence of the substring if found, else returns `-1`	`"hello".rfind("l")` → `3`
`index()`	Similar to `find()`, but raises `ValueError` if the substring is not found	`"hello".index("e")` → `1`
`rindex()`	Similar to `rfind()`, but raises `ValueError` if the substring is not found.	`"hello".rindex("l")` → `3`
`startswith()`	Returns `True` if the string starts with the specified prefix	`"hello".startswith("he")` → `True`
`endswith()`	Returns `True` if the string ends with the specified suffix	`"hello".endswith("lo")` → `True`
`count()`	Returns the number of occurrences of a substring	`"hello".count("l")` → `2`

(3) String Modification and Replacement Methods

Method	Description	Example
`replace()`	Replaces all occurrences of a substring with another string	`"hello".replace("l", "t")` → `"hetto"`
`strip()`	Removes leading and trailing characters (whitespace by default)	`" hello ".strip()` → `"hello"`
`lstrip()`	Removes leading characters (whitespace by default)	`"llama".lstrip("l")` → `"ama"`
`rstrip()`	Removes trailing characters (whitespace by default)	`"buzz".rstrip("z")` → `"bu"`
`join()`	Joins elements of an iterator with the string as a separator	`"-".join(['a', 'b', 'c'])` → `"a-b-c"`
`split()`	Splits a string into a list using a delimiter (default: whitespace)	`"a,b,c".split(",")` → `['a', 'b', 'c']`
`rsplit()`	Like `split()`, but splits from the right	`"a,b,c".rsplit(",", 1)` → `['a,b', 'c']`
`splitlines()`	Splits a string at line breaks (`\n`, `\r\n`, etc)	`"a\nb".splitlines()` → `['a', 'b']`
`expandtabs()`	Replaces tabs (`\t`) with spaces (default: 8 spaces per tab)	`"a\tb".expandtabs(5)` → `"a b"`
`encode()`	Converts a string into bytes using a specified encoding (default is UTF-8)	`"hello".encode()` → `b'hello'`
`maketrans()`	Creates a translation map to be used with `translate()`	`str.maketrans("abc", "123")` → `{97: 49, 98: 50, 99: 51}`
`translate()`	Translates characters into a string using a translation map from `maketrans()`	`"abc".translate(str.maketrans("abc", "123"))` → `"123"`
`partition()`	Splits the string at the first occurrence of the separator into a 3-part tuple	`"a,b,c".partition(',')` → `('a', ',', 'b,c')`
`rpartition()`	Splits the string at the last occurrence of the separator into a 3-part tuple	`"a,b,c".rpartition(',')` → `('a,b', ',', 'c')`

(4) String Validation Methods

Method	Description	Example
`isalnum()`	Returns `True` if all characters are alphanumeric (`a-z`, `A-Z`, and `0-9`)	`"abc123".isalnum()` → `True`
`isalpha()`	Returns `True` if all characters are alphabetic (`a-z` and `A-Z`)	`"abc".isalpha()` → `True`
`isascii()`	Returns `True` if all characters are ASCII	`"abc123".isascii()` → `True`
`isdecimal()`	Returns `True` if all characters are decimal digits. Stricter than `isdigit()`	`"123".isdecimal()` → `True`
`isdigit()`	Returns `True` if all characters are digits	`"²5".isdigit()` → `True`
`isnumeric()`	Returns `True` if all characters are numeric	`"Ⅷ".isnumeric()` → `True`
`isidentifier()`	Returns `True` if the string is a valid Python identifier	`"user_age".isidentifier()` → `True`
`islower()`	Returns `True` if all characters are lowercase	`"abc".islower()` → `True`
`isupper()`	Returns `True` if all characters are uppercase	`"ABC".isupper()` → `True`
`istitle()`	Returns `True` if the string follows title case (first letter of each word uppercase)	`"Hello World".istitle()` → `True`
`isspace()`	Returns `True` if all characters are whitespace	`"\n\t".isspace()` → `True`
`isprintable()`	Returns `True` if all characters are printable	`"abc\n".isprintable()` → `False`

(5) Alignment, Padding, and Formatting Methods

Method	Description	Example
`ljust()`	Left-justifies the string with padding (default: space)	`"hi".ljust(5, '-')` → `"hi---"`
`rjust()`	Right-justifies the string with padding (default: space)	`"hi".rjust(5, '-')` → `"---hi"`
`center()`	Centers the string with padding (default: space)	`"hi".center(5, '-')` → `"--hi-"`
`zfill()`	Pads the string with leading zeros to reach a specified width	`"9".zfill(3)` → `"009"`
`format()`	Formats string with placeholders and values	`"Name: {}".format("James")` → `"Name: James"`
`format_map()`	Formats using a dictionary (mapping) of values	`"age: {age}".format_map({"age": 32})` → `"age: 32"`