Strings

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🐍 STRINGS AND STRING FUNCTIONS IN PYTHON

Creating, Accessing, Manipulating and Processing Strings

📘 1. What is a String?

A string is a sequence of characters enclosed within single quotes, double quotes, or triple quotes.

Strings can contain: letters, numbers, spaces, symbols and special characters.

name = "Python"
college = 'Computer Science'
message = """Welcome to Python Programming"""

🔤 2. Creating Strings

str1 = 'Hello'
str2 = "Python"
str3 = '''Programming'''
str4 = """Computer Science"""

Hello
Python
Programming
Computer Science

3️⃣ Single and Double Quotes

a = 'Hello'
b = "World"

print(a)
print(b)

Hello
World

💡 Single quotes and double quotes can both be used to create strings.

4️⃣ Triple-Quoted Strings

Triple quotes are commonly used for multiline strings.

message = """Python
is
easy to learn."""

print(message)

Python
is
easy to learn.

🔒 5. Strings are Immutable

Strings in Python are immutable. This means that individual characters of an existing string cannot be changed directly.

text = "Python"

# text[0] = "J"   # Error

⚠️ A new string must be created if the value needs to be changed.

text = "Python"
text = "J" + text[1:]

print(text)

Jython

6️⃣ String Indexing

Each character has an index position.

text = "PYTHON"

print(text[0])
print(text[1])
print(text[5])

P
Y
N

Character	P	Y	T	H	O	N
Positive Index	0	1	2	3	4	5
Negative Index	-6	-5	-4	-3	-2	-1

7️⃣ String Slicing

text = "PYTHON"

print(text[0:3])
print(text[2:6])
print(text[:4])
print(text[2:])

PYT
THON
PYTH
THON

Syntax: string[start : stop : step]

8️⃣ String Concatenation

The + operator joins two or more strings.

first = "Hello"
second = "Python"

result = first + " " + second

print(result)

Hello Python

9️⃣ String Repetition

The * operator can repeat a string.

print("Python " * 3)

Python Python Python

🔢 10. len() Function

The len() function returns the number of characters in a string.

text = "Python"

print(len(text))

6

🛠️ 11. Important String Functions and Methods

len()
Returns string length.

lower()
Converts characters to lowercase.

upper()
Converts characters to uppercase.

capitalize()
Capitalizes the first character.

title()
Capitalizes the first character of each word.

swapcase()
Swaps uppercase and lowercase characters.

strip()
Removes leading and trailing whitespace.

replace()
Replaces part of a string.

split()
Splits a string into a list.

join()
Joins elements into a string.

find()
Finds the position of a substring.

count()
Counts occurrences.

startswith()
Checks the beginning of a string.

endswith()
Checks the ending of a string.

isdigit()
Checks whether all characters are digits.

isalpha()
Checks whether all characters are alphabetic.

1️⃣2️⃣ lower()

text = "PYTHON"

print(text.lower())

python

1️⃣3️⃣ upper()

text = "python"

print(text.upper())

PYTHON

1️⃣4️⃣ capitalize()

text = "python programming"

print(text.capitalize())

Python programming

1️⃣5️⃣ title()

text = "python programming language"

print(text.title())

Python Programming Language

1️⃣6️⃣ swapcase()

text = "Python"

print(text.swapcase())

pYTHON

1️⃣7️⃣ strip()

text = "   Python   "

print(text.strip())

Python

1️⃣8️⃣ replace()

text = "I like Java"

print(text.replace("Java", "Python"))

I like Python

1️⃣9️⃣ find()

text = "Python Programming"

print(text.find("Program"))

7

The returned value is the starting index of the searched substring. If the substring is not found, find() returns -1.

2️⃣0️⃣ count()

text = "banana"

print(text.count("a"))

3

2️⃣1️⃣ split()

text = "Python is easy"

words = text.split()

print(words)

['Python', 'is', 'easy']

2️⃣2️⃣ join()

words = ["Python", "is", "easy"]

result = " ".join(words)

print(result)

Python is easy

2️⃣3️⃣ startswith() and endswith()

text = "Python Programming"

print(text.startswith("Python"))
print(text.endswith("Programming"))

True
True

2️⃣4️⃣ isalpha()

text = "Python"

print(text.isalpha())

True

2️⃣5️⃣ isdigit()

text = "12345"

print(text.isdigit())

True

🎨 2️⃣6️⃣ String Formatting

String formatting allows values to be inserted into strings.

name = "Bijan"
age = 25

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

My name is Bijan and I am 25 years old.

💡 f-string is a convenient way to insert variables inside a string using { }.

🔐 2️⃣7️⃣ Escape Characters

Escape Character	Meaning
\n	New line
\t	Tab
\\	Backslash
\'	Single quote
\"	Double quote

print("Hello\nPython")
print("Name\tAge")

Hello
Python
Name    Age

⚖️ 2️⃣8️⃣ String Comparison

a = "apple"
b = "banana"

print(a == b)
print(a != b)

False
True

Strings can be compared using operators such as ==, !=, <, >, <= and >=.

🔍 2️⃣9️⃣ Membership Operators

text = "Python Programming"

print("Python" in text)
print("Java" not in text)

True
True

🎮 3️⃣0️⃣ Interactive String Demonstration

Click a button to see a common string operation.

Result will appear here...

✅ Advantages of Strings in Python

• Easy to create and manipulate.
• Large number of built-in methods are available.
• Supports indexing and slicing.
• Supports Unicode characters.
• Useful for text processing.
• Can be combined using concatenation.
• Useful in web development, data processing and file handling.
• Immutable nature makes strings predictable and safe to use.

❌ Limitations of Strings

• Individual characters cannot be changed directly.
• Repeated string modification may create new string objects.
• Very large text processing may require efficient techniques.
• Incorrect indexing can produce an IndexError.

📋 Important String Functions / Methods at a Glance

Function / Method	Purpose	Example
len()	Find length	len("Python")
lower()	Lowercase	"PYTHON".lower()
upper()	Uppercase	"python".upper()
capitalize()	Capitalize first character	"python".capitalize()
title()	Title case	"python language".title()
strip()	Remove surrounding whitespace	" Python ".strip()
replace()	Replace text	"Java".replace("Java","Python")
find()	Find substring position	"Python".find("th")
count()	Count occurrences	"banana".count("a")
split()	Split into list	"A B C".split()
join()	Join strings	"-".join(["A","B"])
startswith()	Check beginning	"Python".startswith("Py")
endswith()	Check ending	"Python".endswith("on")
isalpha()	Check alphabetic characters	"Python".isalpha()
isdigit()	Check digits	"123".isdigit()

🎯 Important Points for Examination

1. A string is a sequence of characters.
2. Strings can be enclosed in single, double or triple quotes.
3. Python strings are immutable.
4. String indexing starts from 0.
5. Negative indexing starts from -1.
6. String slicing uses [start:stop:step].
7. len() returns the length of a string.
8. lower() converts a string to lowercase.
9. upper() converts a string to uppercase.
10. split() converts a string into a list.
11. join() joins elements into a string.
12. find() returns the position of a substring.
13. replace() replaces one substring with another.
14. isalpha() checks alphabetic characters.
15. isdigit() checks whether all characters are digits.

📌 Quick Summary

Concept	Example
Create String	"Python"
Indexing	"Python"[0]
Slicing	"Python"[0:3]
Length	len("Python")
Uppercase	"python".upper()
Lowercase	"PYTHON".lower()
Replace	"Java".replace("Java","Python")
Split	"A B".split()
Join	"-".join(["A","B"])
Find	"Python".find("th")

© Python Programming Educational Notes | Created by Bijan Krishna Paul

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