Are Python strings mutable?

No. Python str objects are immutable, so every method that appears to change a string actually returns a new string and leaves the original unchanged. For example s.upper() does not modify s; you must assign the result, like s = s.upper(). This is why methods such as replace and strip return a value rather than acting in place.

What is the difference between strip, lstrip, and rstrip?

strip removes leading and trailing characters, lstrip removes only leading ones, and rstrip removes only trailing ones. By default they remove whitespace, but you can pass a string of characters to remove any of those from the relevant end. The argument is a set of characters, not a prefix or suffix, so strip('ab') removes any a or b, not the literal 'ab'.

How do I remove a prefix or suffix instead of characters?

Use removeprefix and removesuffix, added in Python 3.9. Unlike strip, they remove the exact substring once if it is present and otherwise return the string unchanged. So 'test.py'.removesuffix('.py') gives 'test', whereas rstrip('.py') would strip any trailing p, y, or dot character and corrupt the result.

What is the difference between find and index?

Both locate the first occurrence of a substring and return its position. The difference is on failure: find returns -1 when the substring is absent, while index raises a ValueError. Use find when a missing substring is expected and you want to test the result; use index when absence is a genuine error you want to surface.

Is this the complete list of str methods?

It covers every standard str method in current Python 3 across case, search, split and join, trim and pad, testing, and encoding. A few rarely-used methods like maketrans are noted. For exact version availability and edge-case behavior, consult the official Python documentation's Text Sequence Type page.

What is the Python String Methods Reference?

Searchable reference for every Python str method — case, search, split, strip, replace, encode, and format — with each method's signature, return type, and behavior notes. It runs free in your browser on Gera Tools, with nothing uploaded.

Python String Methods Reference

Name: Python String Methods Reference
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Python’s str type is immutable, so every method here returns a new string rather than changing the original. The methods cover case conversion, searching, splitting and joining, trimming, testing, and encoding. This is a searchable offline reference.

Method groups

Because strings are immutable, a call like s.upper() produces a new string — you must assign it (s = s.upper()) to keep the result. The methods fall into six groups:

Case — upper, lower, title, capitalize, casefold, swapcase.
Search — find, index, count, startswith, endswith. find returns -1 on failure; index raises ValueError.
Split / join — split, rsplit, splitlines, partition, join.
Trim / pad — strip, lstrip, rstrip, removeprefix, removesuffix, center, ljust, rjust, zfill.
Test — isalpha, isdigit, isalnum, isspace, isidentifier, etc.
Transform — replace, translate, format, format_map, encode.

Worked examples

"  Hello, World  ".strip().lower().replace(",", "")
# -> 'hello world'

"file.tar.gz".removesuffix(".gz")  # -> 'file.tar'
"report_2026_q1.csv".split("_")    # -> ['report', '2026', 'q1.csv']
", ".join(["apples", "oranges", "pears"])  # -> 'apples, oranges, pears'
"$19.99".lstrip("$")               # strips any leading $, or any char in the set

strip vs removeprefix / removesuffix

This is the most common source of subtle bugs with string trimming:

"file.py".rstrip(".py")        # -> 'fil'   (removes p, y, . individually — WRONG)
"file.py".removesuffix(".py")  # -> 'file'  (removes exact suffix — CORRECT)

strip, lstrip, and rstrip interpret their argument as a set of characters to remove, not a literal prefix or suffix. Each character in the argument is stripped from the relevant end as long as it matches. Use removeprefix and removesuffix (Python 3.9+) whenever you want to remove an exact string.

split and join: complementary operations

split breaks a string into a list; join reassembles a list into a string. Note that join is called on the separator, not the list:

parts = "a,b,c".split(",")    # -> ['a', 'b', 'c']
"|".join(parts)                # -> 'a|b|c'

split() with no argument splits on any whitespace and drops empty strings — useful for normalizing ragged input. split(",") keeps empty strings between consecutive delimiters.

find vs index

Both locate the first occurrence of a substring and return its position as an integer. The difference matters only on failure:

"hello".find("z")    # -> -1   (no exception)
"hello".index("z")   # raises ValueError

Use find when absence is expected and you want to test the result with if pos != -1. Use index when absence is a genuine error that should surface immediately.

Notes

str.join is called on the separator: ", ".join(items).
casefold() is more aggressive than lower() for case-insensitive comparison of non-ASCII text (e.g., the German ß folds to ss).
This reference covers the standard str methods. For exact version availability consult the official Python docs.