Python Strings

Focus on how the names, objects, and calculations change. We’ll inspect the printed output in the next section.

Choose a different sample input, then follow every step through to the output. Before revealing it, predict what the program will display.

name = 'Ada'
first = name[0]
greeting = "Hello, " + name
print(first)
print(greeting)

A string in Python is a sequence of characters enclosed in single ('), double ("), or triple quotes (''' or """).

'Hello, World!'
"Hello, World!"

Strings are used to store text-based information such as names, messages, or any human-readable data.

You can create a string using single or double quotes interchangeably:

name = 'Arjun'
message = "Hello, World!"

If your string contains quotes inside, use the other type to avoid syntax errors:

quote = "It's a beautiful day"
alt_quote = 'He said, "Hi!"'

Use triple quotes when you want to write strings across multiple lines.

poem = """Roses are red,
Violets are blue,
Python is great,
And so are you."""

In Python, you can access individual characters in a string using indexing. Each character in the string has a position, called an index, which starts from 0 for the first character and increases by one for each subsequent character.

Here's how you can use positive indexing to access characters from the beginning:

greeting = "Hello"
print(greeting[0])  # H (first character)
print(greeting[4])  # o (fifth character)

H
o

Python also supports negative indexing, which allows you to access characters from the end of the string. The last character has an index of -1, the second last is -2, and so on.

greeting = "Hello"
print(greeting[-1])  # o (last character)
print(greeting[-2])  # l (second last character)

o
l

This flexibility makes it easy to access both ends of a string without needing to know its exact length.

Slicing helps extract parts of a string using the syntax string[start:end].

text = "Python"
print(text[0:2])   # Py
print(text[2:])    # thon
print(text[:3])    # Pyt
print(text[-3:])   # hon

Py
thon
Pyt
hon

Strings in Python are immutable. This means once created, they cannot be changed in place.

word = "Python"
word[0] = "J"  # This will raise a TypeError

Traceback (most recent call last):
  File "main.py", line 2, in 
    word[0] = "J"  # This will raise a TypeError
TypeError: 'str' object does not support item assignment

Python provides several built-in methods to work with strings:

• lower(): Converts all characters to lowercase
• upper(): Converts all characters to uppercase
• strip(): Removes leading and trailing whitespace
• replace(old, new): Replaces substring
• split(): Splits the string into a list
• join(): Joins elements of a list with a string separator

s = "  Learn Python  "
print(s.strip())        # 'Learn Python'
print(s.lower())        # '  learn python  '
print(s.replace("Python", "Java"))  # '  Learn Java  '

Learn Python
  learn python  
  Learn Java  

For complete set of string methods in Python, you may refer String methods.

In Python, you can insert variables directly into strings using f-strings (formatted string literals). This makes it easy to construct readable and dynamic messages.

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

My name is Arjun and I am 25 years old.

Python allows you to check whether a certain substring exists within a string using the in and not in keywords. These return a boolean value — True or False.

msg = "Welcome to Python"
print("Python" in msg)     # True, because "Python" is in the string
print("Java" not in msg)   # True, because "Java" is not in the string

True
True

Since strings are sequences of characters, you can loop through them using a for loop. Each iteration gives you one character from the string.

for char in "Hi":
    print(char)

H
i

You can find out how many characters are in a string using the built-in len() function. This includes letters, digits, spaces, and symbols.

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

6

Before working with strings, you might want to validate them:

• isalpha() – checks if all characters are alphabets
• isdigit() – checks if all characters are digits
• isalnum() – checks if all characters are alphanumeric
• isspace() – checks for only whitespace

val = "123abc"
print(val.isalnum())  # True
print(val.isdigit())  # False

True
False

Connect what you noticed in the example with the idea below.