🐍1.1String in Python - Interview Explanation detail

What is a String in Python? A string in Python is an immutable sequence of characters enclosed within single (' or "), double (" or "), or triple quotes (''' or """). It is a fundamental data type used to represent text.

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Characteristics of Python Strings:

• Immutable – Once created, they cannot be modified.
• Indexed & Slicable – Strings support indexing (s[0]) and slicing (s[1:4]).
• Dynamic Typing – No need to declare the type explicitly.
• Unicode Support – Python strings support Unicode characters.
• Strings are indexed, meaning you can access characters using their position (positive and negative indexing).

Slicing extracts parts of a string using string[start:end:step].

• start (default=0) → Inclusive (included in the result)
• end (default=last index) → Exclusive (not included in the result)
• step → Optional, defines the jump

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1. String Creation

# Single and Double Quotes
s1 = 'Hello'
s2 = "World"

# Triple Quotes for Multiline String
s3 = '''This is
a multiline
string.'''

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2. Accessing String Elements

s = "Python"
print(s[0])  # Output: P (Positive Indexing)
print(s[-1]) # Output: n (Negative Indexing)

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3. String Slicing

s = "Python"
print(s[0:4])   # Output: Pyth (from index 0 to 3)
print(s[:4])    # Output: Pyth (default start=0)
print(s[2:])    # Output: thon (default end=last index)
print(s[::2])   # Output: Pto (every 2nd character)

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4. String Methods

Case Conversion

s = "hello world"
print(s.upper())       # HELLO WORLD
print(s.lower())       # hello world
print(s.title())       # Hello World
print(s.capitalize())  # Hello world
print(s.swapcase())    # HELLO WORLD

Checking & Searching

s = "Hello Python"
print(s.startswith("Hello"))  # True
print(s.endswith("Python"))   # True
print(s.find("Py"))  # 6 (index of first occurrence)
print(s.count("o"))  # 2 (count of 'o')

Modification

s = " Python "
print(s.strip())  # "Python" (removes spaces from both sides)
print(s.lstrip()) # "Python " (removes left spaces)
print(s.rstrip()) # " Python" (removes right spaces)

Replacing & Splitting

s = "Hello, World"
print(s.replace("World", "Python"))  # Hello, Python

s = "Python is fun"
print(s.split())  # ['Python', 'is', 'fun'] (default split on space)

s = "one,two,three"
print(s.split(","))  # ['one', 'two', 'three']

Python split() Method Table

Method	Description
string.split()	Splits by spaces (default).
string.split(",")	Splits using a comma.
string.split("\n")	Splits by newlines.
string.split(" ", 2)	Splits only twice.
re.split(r"[;, ]", s)	Splits using multiple delimiters.

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5. String Concatenation and Repetition

s1 = "Hello"
s2 = "World"
print(s1 + " " + s2)  # Hello World (Concatenation)
print(s1 * 3)  # HelloHelloHello (Repetition)

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6. String Formatting

Using f-strings (Python 3.6+)

name = "Alice"
age = 25
print(f"My name is {name} and I am {age} years old.")

Using .format() Method

print("My name is {} and I am {} years old.".format(name, age))

Using % Operator

print("My name is %s and I am %d years old." % (name, age))

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7. String Encoding & Decoding

s = "Hello"
encoded_s = s.encode("utf-8")  # Encoding to bytes
print(encoded_s)  # b'Hello'

decoded_s = encoded_s.decode("utf-8")  # Decoding back to string
print(decoded_s)  # Hello

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8. String Immutability

s = "Python"
s[0] = "J"  # Raises an error (strings are immutable)

To modify, create a new string:

s = "J" + s[1:]
print(s)  # Jython

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9. Reversing a String

s = "Python"
print(s[::-1])  # nohtyP

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10. Checking If a String is a Palindrome

def is_palindrome(s):
    return s == s[::-1]

print(is_palindrome("madam"))  # True
print(is_palindrome("hello"))  # False