Python Strings: Methods and Slicing Explained

A Python string (str) is an immutable sequence of characters. You create one with quotes, read parts of it with indexes and slices (s[0], s[1:4]), and change it with methods such as upper(), strip(), split() and replace(). Every method returns a new string, because the original can never be changed.

This guide covers creating strings, slicing, the methods you will use most, f-string formatting and the mistakes that trip people up, with real output for every example.

Creating strings

Single and double quotes do the same thing. Pick whichever avoids escaping: "It's fine" needs no backslash. Triple quotes let a string run across several lines. A backslash starts an escape such as \n for a new line, and a raw string (r"...") turns escapes off, which is handy for Windows paths and regular expressions.

single = 'Hello'
double = "It's fine"
multi = """Line one
Line two"""
print(single, double)
print(multi)
print("a\nb")
print(r"C:\new\table")

Output

Hello It's fine
Line one
Line two
a
b
C:\new\table

Indexing and slicing

Each character has a position. Counting starts at 0 from the left, and at -1 from the right:

A slice s[start:stop:step] takes the characters from start up to, but not including, stop. Leave a part out and Python fills in a sensible default:

s = "Python"
print(s[0], s[-1])
print(s[1:4])
print(s[:2], s[2:])
print(s[::2])
print(s[::-1])
print(s[10:20] == "")

Output

P n
yth
Py thon
Pto
nohtyP
True

Read them like this: s[1:4] is positions 1, 2 and 3. s[:2] means “from the start to position 2”. s[::2] takes every second character. s[::-1] steps backwards, which reverses the string.

One difference is worth remembering. Asking for a single position that does not exist is an error, but a slice that runs past the end is quietly shortened:

s = "Python"
print(s[6])

Output

IndexError: string index out of range

That is why s[10:20] in the example above simply gave an empty string instead of failing.

The string methods you will use most

Methods are functions attached to a string, called with a dot. These cover most day-to-day work: cleaning text, splitting it up and putting it back together.

text = "  Hello, World  "
print(text.strip())
print(text.strip().lower())
print(text.strip().upper())
print("hello world".title())
print("a,b,c".split(","))
print("-".join(["2026", "09", "25"]))
print("banana".replace("a", "o"))
print("banana".count("a"))

Output

Hello, World
hello, world
HELLO, WORLD
Hello World
['a', 'b', 'c']
2026-09-25
bonono
3

split() turns a string into a list, and join() does the reverse. Notice that join() is called on the separator ("-".join(...)), not on the list. That trips up almost everyone the first time.

Searching inside a string

s = "data analytics"
print(s.find("an"))
print(s.find("xyz"))
print(s.startswith("data"), s.endswith("ics"))
print("lyt" in s)

Output

5
-1
True True
True

find() returns the position of the first match, or -1 if there is none. Its cousin index() does the same but raises an error when the text is missing, so use find() when “not found” is a normal outcome:

print("data".index("z"))

Output

ValueError: substring not found

To simply check whether text is present, use the in operator, as in "lyt" in s. It reads naturally and returns True or False.

Formatting with f-strings

An f-string is a string with an f in front. Anything inside curly braces is evaluated and inserted. After a colon you can control how it looks: decimals, thousands separators, alignment and width.

name = "Asha"
score = 91.456
big = 1234567
print(f"{name} scored {score:.1f}%")
print(f"{big:,}")
print(f"[{name:>8}] [{name:<8}] [{name:^8}]")
print(f"{score=}")

Output

Asha scored 91.5%
1,234,567
[    Asha] [Asha    ] [  Asha  ]
score=91.456

:.1f means one decimal place, :, adds thousands separators, and >8, <8, ^8 right-align, left-align and centre inside a width of 8. The {score=} form (Python 3.8 and later) prints the name and the value, which is a quick way to debug.

Strings are immutable

You cannot change a character inside a string (s[0] = "B" raises a TypeError, as we saw in Python Data Types Explained). More important is what that means for methods: calling s.upper() does not change s. It hands you a new string, and if you ignore it, nothing happens:

s = "hello"
s.upper()
print(s)
s = s.upper()
print(s)

Output

hello
HELLO

The first print still shows hello. Only after we assign the result back with s = s.upper() does the name point at the new value.

Everyday string tasks

A few short recipes that come up constantly, and in interviews:

word = "Level"
print(word[::-1])
print(word.lower() == word.lower()[::-1])
vowels = sum(1 for ch in "education" if ch in "aeiou")
print(vowels)
messy = "  too   many   spaces "
print(messy.split())
print(" ".join(messy.split()))

Output

leveL
True
5
['too', 'many', 'spaces']
too many spaces

• Reverse a string: s[::-1].
• Palindrome check: compare the lower-cased string with its reverse.
• Count vowels: loop through the characters and test ch in "aeiou".
• Collapse extra spaces: " ".join(text.split()). Calling split() with no argument splits on any run of whitespace and drops the empty pieces.

Common mistakes

Mistake 1: expecting strip() to remove a word

strip(), lstrip() and rstrip() take a set of characters, not a prefix or suffix. They keep removing any of those characters until they meet one that is not in the set:

print("hehe_x".lstrip("he"))
print("hehe_x".removeprefix("he"))

Output

_x
he_x

lstrip("he") removed every leading h and e, so both “he” pairs went. To remove an exact prefix or suffix use removeprefix() and removesuffix() (Python 3.9 and later).

Mistake 2: forgetting the stop position is excluded

s[1:4] gives three characters, not four. A handy check: the length of a slice is stop - start.

Mistake 3: building a long string with += in a loop

Writing result += piece inside a big loop works, but it creates a new string every time. Collect the pieces in a list and join once at the end: "".join(pieces). It is cleaner and scales better.

Mistake 4: assuming len() counts what you see

len() counts Unicode code points, and one visible character in some scripts is made of several:

print(len("hello"))
print(len("नमस्ते"))

Output

5
6

The Hindi word looks like four or five characters on screen, but Python counts six code points (some are combining marks). For everyday English text the two counts match.

Method cheat sheet

Every row in the table above, checked by running it

ok

Try it yourself

Work out each answer first, then open the solution.

1. What does "python"[1:-1] return?

ytho

2. Reverse every word in "sql is fun", keeping the word order.

print(" ".join(w[::-1] for w in "sql is fun".split()))

lqs si nuf

3. What does "a-b-c".split("-", 1) return?

['a', 'b-c']

4. What does print("ab" * 3, "-" * 5) print?

ababab -----

Paste any of these into our free Python compiler and experiment.

Frequently asked questions

How do I reverse a string in Python?

Use slicing with a step of -1: s[::-1]. It returns a new reversed string and leaves the original unchanged.

How do I check if a string contains a substring?

Use the in operator: "lyt" in text returns True or False. Use find() if you also need the position.

What is the difference between find() and index()?

Both return the position of the first match. When the text is missing, find() returns -1, while index() raises a ValueError.

Are strings mutable in Python?

No. A string cannot be changed after it is created. Methods like upper() and replace() return a new string, so assign the result to a name if you want to keep it.

How do I convert a string to a list and back?

list("abc") gives a list of characters, and "a b c".split() gives a list of words. To go back, use "".join(chars) or " ".join(words).

How do I remove whitespace from a string?

strip() removes it from both ends, lstrip() from the left and rstrip() from the right. To remove extra spaces between words, use " ".join(text.split()).

Related reading

• Python Data Types Explained With Examples – where str fits among the other types.
• Python List Comprehension Explained Simply – build lists from strings in one line.
• Mutable vs Immutable Objects in Python – why strings cannot change in place.
• How to Learn Python: A Step-by-Step Roadmap – the full learning path.