Python string
Introduction
This lesson provides a comprehensive overview of Python strings, a fundamental data type in Python programming. It covers the basics of string creation, manipulation, and various methods available for working with strings. Readers will gain insights into the immutability of strings, slicing techniques, and essential operations such as concatenation and repetition. The lesson also explores advanced topics like string formatting, Unicode representation, and string modification techniques.
Table of Contents
What is The Python string ?
In Python, a string is a sequence of characters enclosed within single quotes (‘…’) or double quotes (“…”).
For example:
my_string = 'Hello, world!'
Python also supports triple-quoted strings (”’…”’ or “””…”””) which can span multiple lines.
For example:
my_string = '''This is a multi-line string.'''
Strings are immutable in Python, which means that once a string is created, it cannot be modified. However, you can create new strings by concatenating two or more strings using the + operator or by repeating a string using the * operator.
For example:
my_string = 'Hello, ' + 'world!' print(my_string) # Output: Hello, world! my_string = 'Python ' * 3 print(my_string) # Output: Python Python Python
Python provides a rich set of string manipulation methods, including methods for splitting a string, replacing substrings, and converting the case of a string.
Here are some examples:
my_string = 'Hello, world!'
print(my_string.split(',')) # Output: ['Hello', ' world!']
my_string = 'Hello, world!'
print(my_string.replace('world', 'Python')) # Output: Hello, Python!
my_string = 'Hello, world!'
print(my_string.upper()) # Output: HELLO, WORLD!You can also access individual characters in a string using indexing, like this:
my_string = 'Hello, world!' print(my_string[0]) # Output: H my_string = 'Hello, world!' print(my_string[0]) # Output: H
Strings in Python are Unicode by default, which means that they can include characters from any language or script.
Here are some additional features and operations related to Python strings:
Formatting strings in python
Python provides different ways to format strings.
One common method is to use the format() method, which allows you to insert values into a string by using placeholders that are replaced with values at runtime.
For example:
name = "Alice"
age = 30
message = "My name is {}, and I am {} years old".format(name, age)
print(message) # Output: My name is Alice, and I am 30 years old
Python 3.6 introduced f-strings, which provide an even more concise and readable way to format strings by including expressions inside curly braces {}.
For example:
name = "Alice"
age = 30 message = f"My name is {name}, and I am {age} years old"
print(message)
# Output: My name is Alice, and I am 30 years oldString slicing in python
You can extract a substring from a string by using slicing. Slicing allows you to specify the start and end indices of the substring you want to extract.
For example:
my_string = "Hello, world!" substring = my_string[0:5]# Extracts the first 5 characters print(substring) # Output: Hello
You can also use negative indices to slice a string from the end.
For example:
my_string = "Hello, world!" substring = my_string[-6:] # Extracts the last 6 characters print(substring) # Output: world!
String concatenation and repetition
You can concatenate two or more strings using the + operator, or repeat a string multiple times using the * operator.
For example
greeting = "Hello" name = "Alice" message = greeting + ", " + name + "!" print(message) # Output: Hello, Alice! separator = "-" * 10 print(separator) # Output: ----------
String methods
Python provides many built-in methods for manipulating strings, such as strip() to remove whitespace from the beginning and end of a string, lower() and upper() to convert the case of a string, startswith() and endswith() to check if a string starts or ends with a particular substring, and many more.
Here are some examples:
my_string = " Hello, world! "
stripped_string = my_string.strip()
print(stripped_string) # Output: Hello, world!
my_string = "Hello, world!"
uppercase_string = my_string.upper()
print(uppercase_string) # Output: HELLO, WORLD!
my_string = "Hello, world!"
starts_with_hello = my_string.startswith("Hello")
print(starts_with_hello) # Output: TrueUnicode strings
- Python strings are Unicode by default, which means they can contain characters from any language or script.
- You can use Unicode escape sequences to represent characters that cannot be directly entered on your keyboard, such as emojis or non-Latin characters.
For example:
my_string = "I Python" print(my_string) # Output: I Python my_string = "\u03A9" print(my_string) # Output: Ω
How to modify string in python?
- In Python, strings are immutable, which means that once a string is created, you cannot modify its contents.
- However, you can create a new string by modifying the original string using various string manipulation methods.
Here are some examples:
Changing case
You can convert a string to lowercase or uppercase using the lower() and upper() methods, respectively.
For example:
my_string = "Hello, world!" lowercase_string = my_string.lower() uppercase_string = my_string.upper() print(lowercase_string) # Output: hello, world! print(uppercase_string) # Output: HELLO, WORLD!
Replacing substrings
- You can replace a substring in a string using the
replace()method. - This method takes two arguments: the substring to be replaced and the replacement string.
For example:
my_string = "Hello, world!"
new_string = my_string.replace("world", "Python")
print(new_string) # Output: Hello, Python!Splitting strings
- You can split a string into a list of substrings using the
split()method. - By default, this method splits the string on whitespace characters, but you can specify a different separator by passing it as an argument.
For example
my_string = "Hello, world!"
split_string = my_string.split(", ")
print(split_string) # Output: ['Hello', 'world!']Stripping whitespace
You can remove whitespace characters from the beginning and/or end of a string using the strip(), lstrip(), and rstrip() methods. strip() removes whitespace from both ends, while lstrip() and rstrip() remove whitespace from the left and right ends, respectively.
For example:
my_string = " Hello, world! " stripped_string = my_string.strip() print(stripped_string) # Output: Hello, world!
Joining strings
You can join a list of strings into a single string using the join() method.
This method takes a list of strings as an argument and returns a string in which the strings in the list are concatenated with the separator string.
For example:
my_list = ["Hello", "world!"] my_string = ", ".join(my_list) print(my_string) # Output: Hello, world!
Summary:
This lesson is a comprehensive guide to understanding and mastering Python strings. From the basics of string creation to advanced topics like Unicode representation and modification techniques, readers will gain practical insights and hands-on experience. Whether you’re new to programming or looking to enhance your Python skills, this lesson provides a solid foundation for working with strings in Python.
Python String Quiz
1-What is a string in Python?
A. A numeric data type
B. A sequence of characters enclosed in single or double quotes
C. A list of integers
D. A Boolean data type
2-How do you create a multi-line string in Python?
A. Using single quotes
B. Using double quotes
C. Using triple quotes (”’…”’ or “””…”””)
D. Using square brackets
3-Strings in Python are:
A. Mutable
B. Immutable
C. Dynamic
D. Constant
4-Which operator is used for string concatenation in Python?
A. *
B. /
C. +
D. –
5-What is the output of the following code?
my_string = ‘Python ‘ * 3
print(my_string)
A. PythonPythonPython
B. Python Python Python
C. Python3
D. Error
6-How can you access the first character of a string in Python?
A. my_string.first()
B. my_string[0]
C. my_string.get(0)
D. my_string.start()
7-Which method is used to split a string into a list of substrings?
A. split()
B. concat()
C. divide()
D. break()
8-What is the output of the following code?
python
Copy code
my_string = ‘Hello, world!’
print(my_string.replace(‘world’, ‘Python’))
A. Hello, world!
B. Hello, Python!
C. Python, world!
D. Error
9-How do you format strings in Python using placeholders?
A. Using triple quotes
B. Using f-strings
C. Using square brackets
D. Using the format() method
10-What is the purpose of the strip() method in Python?
A. Convert the string to uppercase
B. Remove whitespace from both ends of the string
C. Split the string into a list of substrings
D. Replace a substring in the string
11-Which escape sequence represents the Unicode character Ω (Omega)?
A. \u0394
B. \u03A9
C. \u221E
D. \u03B1
12-How do you check if a string starts with the substring “Hello” in Python?
A. my_string.starts(“Hello”)
B. my_string.startswith(“Hello”)
C. my_string.check(“Hello”)
D. my_string.begins(“Hello”)
13-In Python, strings are Unicode by default. What does this mean?
A. Strings can only contain ASCII characters.
B. Strings can include characters from any language or script.
C. Strings cannot be used with Unicode characters.
D. Strings can only contain numeric characters.
14-Which method is used to convert a string to uppercase in Python?
A. toUpper()
B. uppercase()
C. upper()
D. toUpperCase()
15-How do you create an f-string in Python?
A. Using triple quotes
B. Using single quotes
C. Using square brackets
D. By prefixing the string with ‘f’ or ‘F’
Answers:
B, 2. C, 3. B, 4. C, 5. A, 6. B, 7. A, 8. B, 9. D, 10. B, 11. B, 12. B, 13. B, 14. C, 15. D
Quiz 2
1-Which method is used to find the length of a string in Python?
A. size()
B. length()
C. count()
D. len()
2-What is the purpose of string slicing in Python?
A. To concatenate strings
B. To extract a substring from a string
C. To convert a string to uppercase
D. To check if a string starts or ends with a particular substring
3-In Python, how do you represent a newline character in a string?
A. \n
B. \t
C. \r
D. \b
4-What will be the output of the following code?
my_string = “Hello, world!”
print(my_string[::-1])
A. dlrow ,olleH
B. Hello, world!
C. !dlrow ,olleH
D. Error
5-How can you check if a substring is present in a given string?
A. substring()
B. in
C. contains()
D. includes()
6-What is the purpose of the join() method in Python?
A. To concatenate two strings
B. To join a list of strings into a single string
C. To split a string into a list of substrings
D. To replace substrings in a string
7-Which of the following methods is used to check if a string ends with a specific substring?
A. endsswith()
B. ends()
C. suffix()
D. endswith()
8-How do you extract the last three characters of a string in Python?
A. my_string.last(3)
B. my_string[-3:]
C. my_string.slice(-3)
D. my_string.extract(-3)
9-What is the output of the following code?
my_string = “Hello, world!”
print(my_string.split())
A. [‘Hello,’, ‘world!’]
B. [‘Hello’, ‘world’]
C. ‘Hello, world!’
D. Error
10-In Python, how can you represent a backslash character () in a string?
A. \\
B. \b
C. \n
D. \t
Answers:
16. D, 17. B, 18. A, 19. A, 20. B, 21. B, 22. D, 23. B, 24. B, 25. A