Bytebook Compiler

Python Basics

Strings

Indexing and negative indexes, slicing, immutability, the most useful string methods, searching, splitting and joining, and classic string programs.

3 min read5 runnable examples4-question quiz

A string is an immutable sequence of characters. Single, double or triple quotes all work.

Python
s = "Kalvium"
print(len(s), s[0], s[-1], s[2])        # negative indexes count from the end
print(s[0:3], s[3:], s[:4], s[-3:])     # slices: start included, end excluded
print(s[::-1])                          # step -1 reverses
print(s[::2])                           # every second character
Output
7 K m l
Kal vium Kalv ium
muivlaK
Klim
Try it Yourself
K0a1l2v3i4u5m6s[0]s[-1]
Indexes 0 to 6 from the left; −1 to −7 from the right. s[1:4] is "alv".

Strings are immutable

You cannot change a character in place; build a new string instead:

Python
s = "python"
# s[0] = "P"           # TypeError: 'str' object does not support item assignment
s = "P" + s[1:]
print(s)
Output
Python
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Essential string methods

Method Does Example result
upper(), lower(), title(), capitalize() change case "hi there".title() → Hi There
strip(), lstrip(), rstrip() remove whitespace (or given characters) " hi ".strip() → hi
split(sep) split into a list "a,b,c".split(",") → ['a', 'b', 'c']
sep.join(list) join a list into a string "-".join(["a","b"]) → a-b
replace(old, new) replace all occurrences "aaa".replace("a","b") → bbb
find(sub) / index(sub) position of sub (find gives −1 if missing) "hello".find("l") → 2
count(sub) occurrences "banana".count("a") → 3
startswith, endswith prefix / suffix tests
isdigit, isalpha, isalnum, isspace, isupper character class tests
Python
email = "  Asha.Rao@Example.COM "
clean = email.strip().lower()
user, domain = clean.split("@")
print(clean, user, domain)
print(clean.endswith(".com"), clean.count("a"), clean.find("rao"))

words = "data structures and algorithms".split()
print(words)
print(" ".join(w.capitalize() for w in words))
print("-".join(["2026", "11", "14"]))
Output
asha.rao@example.com asha.rao example.com
True 4 5
['data', 'structures', 'and', 'algorithms']
Data Structures And Algorithms
2026-11-14
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Looping over strings

Python
text = "Hello, World 2026!"
letters = digits = spaces = others = 0
for ch in text:
    if ch.isalpha():
        letters += 1
    elif ch.isdigit():
        digits += 1
    elif ch.isspace():
        spaces += 1
    else:
        others += 1
print(letters, digits, spaces, others)

for i, ch in enumerate("abc"):
    print(i, ch, ord(ch))          # ord gives the Unicode code; chr goes back
print(chr(65), chr(0x20B9))
Output
10 4 2 2
0 a 97
1 b 98
2 c 99
A ₹
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Classic string programs

Python
def is_palindrome(s):
    cleaned = "".join(c.lower() for c in s if c.isalnum())
    return cleaned == cleaned[::-1]

def count_vowels(s):
    return sum(1 for c in s.lower() if c in "aeiou")

def is_anagram(a, b):
    return sorted(a.replace(" ", "").lower()) == sorted(b.replace(" ", "").lower())

def char_frequency(s):
    freq = {}
    for c in s:
        freq[c] = freq.get(c, 0) + 1
    return freq

print(is_palindrome("A man, a plan, a canal: Panama"))
print(count_vowels("Object Oriented Programming"))
print(is_anagram("Listen", "Silent"), is_anagram("Dormitory", "Dirty room"))
print(char_frequency("mississippi"))
Output
True
9
True True
{'m': 1, 'i': 4, 's': 4, 'p': 2}
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Test yourself

4 questions · pick an answer to check it instantly

  1. 1

    For s = "programming", what is s[3:7]?

  2. 2

    What does "banana".find("z") return?

  3. 3

    What does " | ".join(["C", "C++", "Python"]) produce?

  4. 4

    Why does s[0] = "X" fail for a string s?

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