Python Strings- complete notes + interview Q&A

Let’s go step by step and explain Python strings with beginner-friendly examples.

🔹 1. What is a String in Python?

A string is a sequence of characters enclosed in single quotes (”), double quotes (“”), or triple quotes (”’ or “””).

s1 = 'Hello'
s2 = "World"
s3 = '''This is also a string'''

Strings are immutable → once created, they cannot be changed in place.

🔹 2. Common String Methods and Usages

✅ (a) `len()` → Get length of string

text = "Python"
print(len(text))  # 6

✅ (b) Slicing → Extract part of a string

word = "Python"
print(word[0])    # 'P' (first character)
print(word[-1])   # 'n' (last character)
print(word[0:4])  # 'Pyth' (characters 0 to 3)
print(word[2:])   # 'thon' (from index 2 to end)

✅ (c) `replace()` → Replace part of string

msg = "I like Java"
new_msg = msg.replace("Java", "Python")
print(new_msg)  # I like Python

✅ (d) `strip()` → Remove extra spaces

data = "   hello world   "
print(data.strip())   # 'hello world'
print(data.lstrip())  # 'hello world   ' (only left)
print(data.rstrip())  # '   hello world' (only right)

✅ (e) `split()` → Break string into list

sentence = "apple,banana,orange"
fruits = sentence.split(",")
print(fruits)  # ['apple', 'banana', 'orange']

✅ (f) `join()` → Join list into string

words = ["Python", "is", "fun"]
sentence = " ".join(words)
print(sentence)  # 'Python is fun'

🔹 3. Multi-line Strings

✅ (a) Using `\` at the end of each line

If you want a long string without breaking it:

text = "This is a very long string \
that goes on the next line \
but is still considered one line."
print(text)
# Output: This is a very long string that goes on the next line but is still considered one line.

✅ (b) Using Triple Quotes (`'''` or `"""`)

Triple quotes let you:

Write multi-line text
Include both single and double quotes inside easily

story = """He said, "Python is amazing!"
And I replied, 'Yes, absolutely!'"""
print(story)

This preserves line breaks and quotes.

🔹 4. Triple Quotes for Docstrings

A docstring is a special string used to document functions, classes, or modules.
They are written in triple quotes right after a function/class definition.

def greet(name):
    """
    This function greets the person whose name is passed as an argument.
    
    Parameters:
        name (str): The name of the person.
    
    Returns:
        str: Greeting message
    """
    return f"Hello, {name}!"
    
print(greet("Alice"))

help(greet) will display the docstring.
They make your code self-explanatory and are a best practice in Python.

✅ Summary

len() → get length
slicing → extract parts
replace() → substitute text
strip() → remove spaces
split() & join() → convert between list and string
\ → continue string across lines
''' or """ → multi-line strings, docstrings

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