Understanding Strings in Python: String Slicing, Operations, and Essential Methods

What Are Strings?

In Python, anything you put between single (' ') or double quotes (" ") is called a string. A string is a collection of characters (text data) arranged in a specific order. Strings are often used to work with textual or Unicode data.

---

Example:

name = "Safia"  
print("Hello, " + name)

Output:

Hello, Safia

• You can use either single or double quotes to define strings, and both will work the same.

---

Using Quotes Inside Strings

If you want to include quotation marks inside a string, you can use single quotes for the string and double quotes for the quote, or vice versa.

Example:

print('He said, "I want to eat an apple".')

Output:

He said, "I want to eat an apple".

---

Multiline Strings

For strings that span multiple lines, use triple quotes (''' or """).

Example:

a = """Lorem ipsum dolor sit amet,  
consectetur adipiscing elit,  
sed do eiusmod tempor incididunt  
ut labore et dolore magna aliqua."""  
print(a)

Output:

Lorem ipsum dolor sit amet,  
consectetur adipiscing elit,  
sed do eiusmod tempor incididunt  
ut labore et dolore magna aliqua.

---

Accessing Characters in a String

Strings in Python work like arrays, where each character has an index starting from 0. You can use square brackets [ ] to access specific characters.

Example:

name = "Safia"  
print(name[0])  # Output: S  
print(name[1])  # Output: a

---

Looping Through a String

You can use a for loop to go through each character in a string one by one.

Example:

name = "Safia"  
for character in name:  
    print(character)

Output:

S 
a  
f 
i  
a

---

In summary: Strings are simple and flexible to use in Python. You can use them for handling text, quotes, multiline text, and more!

Practical:

name = "Safia"
friend = "Sadaf"
anotherFriend = 'Amir'
apple = '''He said, 
Hi Harry
hey I am good
"I want to eat an apple'''

print("Hello, " + name)
# print(apple) 
print(name[0])
print(name[1])
print(name[2])
print(name[3])
print(name[4])
# print(name[5]) # Throws an error
print("Lets use a for loop\n")
for character in apple:
    print(character)

String Slicing & Operations on Strings

The len() function is used to find the length of a string (number of characters).

Strings as Arrays

Strings in Python are sequences of characters, which means they can be treated like arrays. You can access individual characters using their index.

Slicing: Using : specifies a range of characters.

Slicing a String

Slicing lets you extract parts of a string by specifying the start and end indices.

Looping Through a String

Since strings are arrays of characters, they can be looped through using a for loop.

# Length of a String
fruit = "Apple"  
len1 = len(fruit)
print("Apple is a", len1, "letter word.")

# Strings as Arrays
pie = "GuavaPie"  
print(pie[:5])    # Output: Guava
print(pie[6])     # Output: i

# Slicing Examples
print(pie[:5])      # Slicing from Start → Output: Guava
print(pie[5:])      # Slicing till End → Output: Pie
print(pie[2:6])     # Slicing in Between → Output: avap
print(pie[-8:])     # Slicing using Negative Index → Output: GuavaPie

# Looping Through a String
alphabets = "ABCDE"
for i in alphabets:
    print(i)

Output:

Apple is a 5 letter word.
Guava
i
Guava
Pie
avap
GuavaPie
A
B
C
D
E

Quick Quiz : (practice)

fruit = "Apple"
appleLen = len(fruit)
print(appleLen)
print(fruit[0:4]) # including 0 but not 4
print(fruit[1:4]) # including 1 but not 4
print(fruit[:5])
print(fruit[0:-3])
print(fruit[:len(fruit)-3])
print(fruit[-1:len(fruit) - 3])
print(fruit[-3:-1])

# Quick Quiz:
nm = "Safia"
print(nm[-4:-2])
# @SafiaKhatoon

Summary of Operations:

• len() → Find the length of a string.

• Slicing: Extract parts of a string using [start:end].

• Negative Indexing: Use negative numbers to access characters from the end of the string.

• Looping: Iterate through each character in the string using a for loop.

Python String Methods

1. upper()
   Converts all characters to uppercase.

1.  text = "hello"
    print(text.upper())  # Output: HELLO
   

2. lower()
   Converts all characters to lowercase.

    text = "HELLO"
    print(text.lower())  # Output: hello
   

3. strip()
   Removes spaces from the beginning and end.

    text = "  Hello World  "
    print(text.strip())  # Output: Hello World
   

4. rstrip()
   Removes specific trailing characters.

    text = "Hello??"
    print(text.rstrip("?"))  # Output: Hello
   

5. replace()
   Replaces parts of the string with something else.

    text = "I love cats"
    print(text.replace("cats", "dogs"))  # Output: I love dogs
   

6. split()
   Splits the string into a list by a separator.

    text = "apple,banana,grape"
    print(text.split(","))  # Output: ['apple', 'banana', 'grape']
   

7. capitalize()
   Capitalizes the first character.

    text = "python is fun"
    print(text.capitalize())  # Output: Python is fun
   

8. center()
   Aligns the string to the center.

    text = "Hello"
    print(text.center(10, "*"))  # Output: ***Hello***
   

9. count()
   Counts how many times a value appears.

    text = "banana"
    print(text.count("a"))  # Output: 3
   

10. endswith()
    Checks if the string ends with a specific value.

    text = "welcome.txt"
    print(text.endswith(".txt"))  # Output: True
    

11. find()
    Finds the index of the first occurrence of a value.

    text = "Hello World"
    print(text.find("World"))  # Output: 6
    

12. isalnum()
    Returns True if the string contains only letters and numbers.

    text = "Python123"
    print(text.isalnum())  # Output: True
    

13. isalpha()
    Returns True if the string contains only letters.

    text = "Python"
    print(text.isalpha())  # Output: True
    

14. islower()
    Returns True if all characters are lowercase.

    text = "python"
    print(text.islower())  # Output: True
    

15. isspace()
    Returns True if the string contains only spaces.

    text = "   "
    print(text.isspace())  # Output: True
    

16. istitle()
    Returns True if each word starts with an uppercase letter.

    text = "Hello World"
    print(text.istitle())  # Output: True
    

17. isupper()
    Returns True if all characters are uppercase.

    text = "HELLO"
    print(text.isupper())  # Output: True
    

18. startswith()
    Checks if the string starts with a specific value.

    text = "Hello Python"
    print(text.startswith("Hello"))  # Output: True
    

19. swapcase()
    Swaps uppercase to lowercase and vice versa.

    text = "Hello World"
    print(text.swapcase())  # Output: hELLO wORLD
    

20. title()
    Converts the first character of each word to uppercase.

    text = "hello python"
    print(text.title())  # Output: Hello Python