In Python, strings are sequences of characters enclosed within single quotes ('), double quotes (") or triple quotes (''' or """). Strings are one of the most commonly used data types in Python.
Creating Strings
You can create strings using:
- Single quotes
- Double quotes
- Triple quotes (used for multi-line strings or documentation strings).
Examples:
# Single Quotes
string1 = 'Hello, World!'
# Double Quotes
string2 = "Python is fun!"
# Triple Quotes (Multi-line String)
string3 = '''This is a multi-line
string in Python.'''
print(string1) # Output: Hello, World!
print(string2) # Output: Python is fun!
print(string3)
# Output:
# This is a multi-line
# string in Python.
Accessing Strings
Strings are indexed and can be accessed using their position.
- Indexing starts at
0(left to right). - Negative indexing starts at
-1(right to left).
Example:
text = "Python"
# Positive Indexing
print(text[0]) # Output: P
print(text[3]) # Output: h
# Negative Indexing
print(text[-1]) # Output: n
print(text[-4]) # Output: t
String Slicing
You can extract portions of a string using slicing. The syntax is:
string[start:stop:step]
start: Starting index (inclusive).stop: Ending index (exclusive).step: Step size (default is1).
Examples:
text = "Python Programming"
# Slice from index 0 to 5
print(text[0:6]) # Output: Python
# Slice with step
print(text[0:12:2]) # Output: Pto rg
# Omitting start (default is 0)
print(text[:6]) # Output: Python
# Omitting stop (default is end of string)
print(text[7:]) # Output: Programming
# Using negative index
print(text[-11:]) # Output: Programming
String Properties
- Immutable: Strings cannot be changed after creation.
Example:text = "hello" text[0] = 'H' # Error: 'str' object does not support item assignment - Concatenation: Use
+to combine strings.
Example:str1 = "Hello" str2 = "World" print(str1 + " " + str2) # Output: Hello World - Repetition: Use
*to repeat strings.
Example:text = "Hi! " print(text * 3) # Output: Hi! Hi! Hi!
Common String Methods
Python provides many built-in methods for string manipulation. Here are some frequently used methods:
| Method | Description | Example |
|---|---|---|
upper() | Converts string to uppercase. | "hello".upper() → "HELLO" |
lower() | Converts string to lowercase. | "HELLO".lower() → "hello" |
title() | Converts to title case (capitalize each word). | "hello world".title() → "Hello World" |
strip() | Removes leading/trailing spaces. | " hello ".strip() → "hello" |
replace() | Replaces a substring with another. | "abc".replace('a', 'z') → "zbc" |
split() | Splits string into a list of words. | "a,b,c".split(',') → ['a', 'b', 'c'] |
join() | Joins elements of a list into a single string. | ",".join(['a', 'b', 'c']) → "a,b,c" |
find() | Returns index of first occurrence of substring. | "hello".find('l') → 2 |
startswith() | Checks if string starts with a specific substring. | "Python".startswith("Py") → True |
endswith() | Checks if string ends with a specific substring. | "Python".endswith("on") → True |
String Formatting
Python provides ways to format strings dynamically:
- Using f-strings (Python 3.6+):
name = "Alice" age = 25 print(f"My name is {name} and I am {age} years old.") # Output: My name is Alice and I am 25 years old. - Using
.format()method:name = "Bob" print("My name is {}.".format(name)) # Output: My name is Bob. - Using
%operator:name = "Eve" age = 30 print("My name is %s and I am %d years old." % (name, age)) # Output: My name is Eve and I am 30 years old.
Escape Characters
Escape characters allow you to include special characters in strings.
| Escape Character | Description | Example |
|---|---|---|
\\ | Backslash | "This is a \\\\" |
\' | Single Quote | 'It\'s great!' |
\" | Double Quote | "He said \"Hi\"" |
\n | New Line | "Hello\nWorld" |
\t | Tab Space | "Hello\tWorld" |
\b | Backspace | "AB\bC" → "AC" |
String Operations
- Checking for Substrings:
text = "Hello, World!" print("Hello" in text) # Output: True print("Python" not in text) # Output: True - Iterating Through Strings:
for char in "Python": print(char) # Output: # P # y # t # h # o # n - String Length: Use
len()to get the number of characters in a string:text = "Hello" print(len(text)) # Output: 5
Practical Examples
Example 1: Reversing a String
text = "Python"
reversed_text = text[::-1] # Slice with step -1
print(reversed_text) # Output: nohtyP
Example 2: Count Vowels in a String
text = "Programming is fun!"
vowels = "aeiouAEIOU"
count = sum(1 for char in text if char in vowels)
print("Number of vowels:", count) # Output: Number of vowels: 5
Example 3: Capitalize Each Word
text = "hello world"
print(text.title()) # Output: Hello World
Summary
- Strings are immutable sequences of characters in Python.
- Use indexing and slicing to access portions of a string.
- String methods help in formatting, modifying, and analyzing strings.
- Use escape sequences for special characters.
- Strings can be formatted dynamically using
f-strings,.format(), or%operator.
This explanation covers Python strings with detailed examples and practical use cases.