Python Strings

Python strings are a key data type for handling text. This article explains how they work, ways to manipulate them, and useful built-in methods. It also covers formatting, slicing, and real-world examples to help you use strings effectively.

Contents:

1. Introduction to Python Strings
2. Creating Strings in Python
3. Accessing Characters in a String in Python
4. Modifying Strings in Python
5. String Immutability in Python
6. String Formatting in Python
7. Updating a String in Python
8. Deleting a String in Python
9. Escape Characters in Python
10. String Methods in Python
11. Raw Strings in Python
12. FAQs on Strings in Python

Introduction to Python Strings

Python strings store and handle text as sequences of characters. They are a widely used data type with many built-in methods for formatting, slicing, and modifying text. You can create strings using single (‘ ‘), double (” “), or triple (”’ ”’ or “”” “””) quotes, making text handling flexible and convenient.

Creating Strings in Python

Strings in Python are sequences of characters enclosed within quotes. They can be created using single, double, or triple quotes.

1. Using Single Quotes

subject = 'Python'
print(subject)

Output:

Python

2. Using Double Quotes

# Sanfoundry Topic Name
topic = "Data Structures"
print(topic)

Output:

Data Structures

3. Using Triple Quotes for Multi-line Strings

# Sanfoundry Quiz Instructions
instructions = '''1. Attempt all questions.
2. No negative marking.'''
print(instructions)

Output:

1. Attempt all questions.
2. No negative marking.

4. Creating an Empty String

# Empty String Declaration
empty_string = ""
print("Length:", len(empty_string))

Output:

Length: 0

5. Creating a String with Escape Characters

course = "Sanfoundry's \"Python\" Course"
print(course)

Output:

Sanfoundry's "Python" Course

Accessing Characters in a String in Python

Strings in Python are sequences of characters that you can access using indexing and slicing techniques.

1. Accessing Characters Using Indexing

Indexing lets you access individual characters based on their position. The first character has an index of 0, while the last character has an index of -1.

text = "Python"
print(text[0])  # First character
print(text[3])  # Fourth character
print(text[-1]) # Last character

Output:

P
h
n

2. Accessing a Range of Characters Using Slicing

Slicing extracts a part of the string using the syntax: string[start:end]. It includes characters from the start index up to end – 1.

topic = "Data Structures"
 
# Accessing substring using slicing
print(topic[0:4])    # First four characters
print(topic[5:])     # Characters from index 5 to the end
print(topic[:4])     # First four characters (same as [0:4])
print(topic[-4:])    # Last four characters

Output:

Data
Structures
Data
ures

3. Using a Loop to Access Each Character

subject = "DBMS"
 
for char in subject:
    print(char, end=" ")

Output:

D B M S

Modifying Strings in Python

Strings in Python are immutable, meaning their content cannot be modified directly. However, you can create modified versions of strings using various techniques.

1. Changing Case Using upper() and lower()

upper() – Converts all characters to uppercase. lower() – Converts all characters to lowercase.

subject = "Python Course"
 
print(subject.upper())  # Convert to uppercase
print(subject.lower())  # Convert to lowercase

Output:

PYTHON COURSE
python course

2. Replacing Substrings Using replace()

The replace() method in Python is used to replace a specific substring within a string with another substring. It does not modify the original string but returns a new modified version.

Syntax:

string.replace(old, new, count)

Example:

course = "Data Structures"
 
# Replace 'Data' with 'Algo'
modified_course = course.replace("Data", "Algo")
print(modified_course)

Output:

Algo Structures

3. Changing a String Using Concatenation

Since strings in Python are immutable, you cannot modify them directly. However, you can create a new string by concatenating existing strings using the + operator.

module1 = "DBMS"
module2 = "OS"
combined = module1 + " and " + module2
print(combined)

Output:

DBMS and OS

4. Removing Whitespace Using strip()

strip() – Removes leading and trailing whitespaces. lstrip() – Removes leading whitespaces. rstrip() – Removes trailing whitespaces.

Example:

topic = "  Python Programming  "
 
print(topic.strip())
print(topic.lstrip())  
print(topic.rstrip())

Output:

Python Programming
Python Programming   
  Python Programming

5. Splitting and Joining Strings

split() – Splits a string into a list of substrings. join() – Joins a list of strings into a single string.

# Sanfoundry Quiz Topics
quiz = "Python, Java, DBMS"
quiz_list = quiz.split(", ")
print(quiz_list)  # Output: ['Python', 'Java', 'DBMS']
 
# Join back to a string
new_quiz = " and ".join(quiz_list)
print(new_quiz)

Output:

['Python', 'Java', 'DBMS']  
Python and Java and DBMS

6. Reversing a String

Strings can be reversed using slicing.

module = "AI"
reversed_module = module[::-1]
print(reversed_module)

Output:

IA

String Immutability in Python

In Python, strings are immutable, meaning you cannot modify their content after creation. Any operation that appears to modify a string actually creates a new string instead of changing the original one.

Example: Strings Cannot Be Modified Directly

text = "Sanfoundry"
text[0] = "H"  # This will cause an error

Error:

TypeError: 'str' object does not support item assignment

Modifying a String Indirectly

To modify a string, you must create a new one using concatenation, replacement, or slicing:

text = "Sanfoundry"
new_text = "H" + text[1:]  # Replacing 'S' with 'H'
print(new_text)    # Output: Hanfoundry

String Formatting in Python

String formatting in Python allows you to insert variables into a string in a flexible and readable way. There are three main methods for string formatting in Python.

1. Using format() Method

The format() method inserts values into placeholders defined by {}.

# Sanfoundry Quiz Details
subject = "Python"
score = 95
 
result = "You scored {} in {} quiz.".format(score, subject)
print(result)

Output:

You scored 95 in Python quiz.

2. Using f-Strings

f-Strings are prefixed with f and allow embedding expressions inside curly braces {}.

# Sanfoundry Course Info
course = "DBMS"
duration = 30
 
info = f"{course} course is for {duration} hours."
print(info)

Output:

You scored 95 in Python quiz.
DBMS course is for 30 hours.

3. Using % Operator (Old Method)

% is used as a placeholder for string, integer, and other data types.

# Sanfoundry Certification Info
cert = "Java"
hours = 40
 
details = "The %s certification requires %d hours." % (cert, hours)
print(details)

Output:

The Java certification requires 40 hours.

4. Aligning Text Using format()

format() can align text using < (left), > (right), and ^ (center).

# Sanfoundry Result Summary
print("{:<10} {:^10} {:>10}".format("Name", "Score", "Grade"))
print("{:<10} {:^10} {:>10}".format("Raj", 90, "A"))
print("{:<10} {:^10} {:>10}".format("Neha", 85, "B"))

Output:

Name         Score       Grade
Raj            90          A
Neha           85          B

5. Formatting Numbers with format()

You can format floating-point numbers with precision.

# Sanfoundry Quiz Time
time_taken = 45.6789
 
formatted_time = "Quiz completed in {:.2f} minutes.".format(time_taken)
print(formatted_time)

Output:

Quiz completed in 45.68 minutes.

Updating a String in Python

Since strings are immutable, you cannot modify a part of a string directly. However, you can assign a new value to the variable instead.

# Original Sanfoundry Subject
subject = "Python"
 
# Updating by creating a new string
subject = "Java"
print("Updated Subject:", subject)

Output:

Updated Subject: Java

Deleting a String in Python

Python allows you to delete a string completely using the del keyword. However, since strings are immutable, you cannot delete individual characters.

# Sanfoundry Course Name
course = "Python"
 
# Deleting the string
del course
 
# Attempting to access the deleted string (will raise an error)
# print(course)  # NameError: name 'course' is not defined

Deleting Multiple Strings

You can delete multiple strings using del with multiple variables.

# Sanfoundry Topics
topic1 = "Java"
topic2 = "Python"
 
# Deleting both topics
del topic1, topic2
 
# Attempting to access deleted strings
# print(topic1)  # NameError
# print(topic2)  # NameError

Error:

NameError: name 'topic1' is not defined

Escape Characters in Python

Escape characters in Python allow you to include special characters in a string that are difficult or impossible to type directly. An escape sequence starts with a backslash (\) followed by a specific character to represent special symbols.

Common Escape Characters

Example:

# Using Escape Characters
print('Sanfoundry\'s Quiz')  # Single quote
print("He said, \"Learn Python!\"")  # Double quote
print("Path to file: C:\\path\\file")  # Backslash
print("Java\nQuiz")  # Newline
print("Python\tProgramming")  # Tab space

Output:

Sanfoundry's Quiz
He said, "Learn Python!"
Path to file: C:\path\file
Java
Quiz
Python   Programming

String Methods in Python

Python provides many built-in string methods to manipulate and process text. Here are some commonly used string methods:

Example:

subj = "  Python Programming  "
 
# 1. strip() - Removes leading and trailing whitespace
print(subj.strip())  # Output: 'Python Programming'
 
# 2. lower() - Converts all characters to lowercase
print(subj.lower())  # Output: '  python programming  '
 
# 3. upper() - Converts all characters to uppercase
print(subj.upper())  # Output: '  PYTHON PROGRAMMING  '
 
# 4. title() - Converts the first letter of each word to uppercase
print(subj.title())  # Output: '  Python Programming  '
 
# 5. replace() - Replaces occurrences of a substring
print(subj.replace("Python", "Java"))  # Output: '  Java Programming  '
 
# 6. split() - Splits the string into a list
print(subj.split())  # Output: ['Python', 'Programming']
 
# 7. join() - Joins elements of a list with a separator
words = ["Hello", "World"]
print(" ".join(words))  # Output: 'Hello World'
 
# 8. find() - Finds the position of a substring
print(subj.find("Programming"))  # Output: 10
 
# 9. count() - Counts occurrences of a substring
print(subj.count("o"))  # Output: 2
 
# 10. startswith() - Checks if the string starts with a specific substring
print(subj.startswith("  Python"))  # Output: True
 
# 11. endswith() - Checks if the string ends with a specific substring
print(subj.endswith("  "))  # Output: True
 
# 12. isalpha() - Checks if all characters are alphabetic (ignores spaces)
print(subj.strip().isalpha())  # Output: False (because of space between words)

String Membership Testing in Python

String membership testing in Python checks whether a substring is present in a given string using the in and not in operators.

1. in Operator – Check if Substring is Present
Returns True if the substring is found.

# Sanfoundry Course Name
course = "Python Programming"
 
# Check if 'Python' is in the string
print("Python" in course)  # Output: True
 
# Check if 'Java' is in the string
print("Java" in course)  # Output: False

2. not in Operator – Check if Substring is NOT Present
Returns True if the substring is not found.

# Sanfoundry Subject Name
subject = "Data Science"
 
# Check if 'AI' is not in the string
print("AI" not in subject)  # Output: True
 
# Check if 'Data' is not in the string
print("Data" not in subject)  # Output: False

3. Case-Sensitive Membership Testing

# Sanfoundry Quiz Topic
quiz = "Machine Learning"
 
# Case-sensitive check
print("machine" in quiz)  # Output: False
print("Machine" in quiz)  # Output: True

Raw Strings in Python

Raw strings in Python are prefixed with r or R and treat backslashes (\) as literal characters. This is useful when dealing with file paths, regular expressions, or escape sequences where you want to avoid interpreting backslashes as escape characters.

# Normal string
path_normal = "C:\\Users\\Sanfoundry\\Documents\\file.txt"
print("Normal String:", path_normal)
 
# Raw string
path_raw = r"C:\Users\Sanfoundry\Documents\file.txt"
print("Raw String:", path_raw)

Output:

Normal String: C:\Users\Sanfoundry\Documents\file.txt
Raw String: C:\Users\Sanfoundry\Documents\file.txt

FAQs on Strings in Python

1. What is a string in Python?
A string in Python is a sequence of characters enclosed in single (‘ ‘), double (” “), or triple (”’ ”’ or “”” “””) quotes. It is used to store and manipulate text.

2. Are strings in Python mutable?
No, Python strings are immutable, meaning their content cannot be changed after creation. However, you can create a modified version of a string using slicing, concatenation, or string methods.

3. How can you access characters in a string?
Characters in a string can be accessed using indexing. The first character has an index of 0, and negative indices can be used to access characters from the end.

4. How do you concatenate two strings?
Strings can be combined using the + operator or the .join() method.

5. How do you repeat a string multiple times?
Using the * operator, a string can be repeated a specified number of times.

6. How do you format a string in Python?
Python provides multiple ways to format strings, including f-strings (f”…”), the .format() method, and the % formatting method.

7. How do you count the occurrences of a character in a string?
The .count() method is used to count how many times a specific character appears in a string.