Python String Indexing & Slicing PDF

String : Indexing and Slicing in Python Strings Indexing and Slicing Overview: Indexing: Accesses a single character in a string using its position (index). Indexes start from 0 for the first character and can be negative fo...

String : Indexing and Slicing in Python Strings Indexing and Slicing Overview: Indexing: Accesses a single character in a string using its position (index). Indexes start from 0 for the first character and can be negative for counting from the end. Example: string gives the first character. Slicing: Extracts a substring from the string using a range of indices. The syntax is string[start:stop:step] , where: start is the index where the slice begins (inclusive). stop is the index where the slice ends (exclusive). step specifies the stride between indices. Example: string[1:4] gives characters from index 1 to 3. Differences: Indexing retrieves individual characters, while slicing retrieves a substring. Indexing uses a single index value, whereas slicing uses start, stop, and step indices. Indexing is useful for accessing a specific character, while slicing is ideal for extracting parts of a string. When to Use: Indexing: When you need a specific character, like extracting the first or last character. String : 1  Slicing: When you need a part of the string, like extracting a word or phrase. Practice Questions 1. Indexing Practice: Given the string s = "Hello, World!" , what is the result of s ? How can you access the last character of the string s = "Python" using indexing? 2. Slicing Practice: For the string s = "Programming" , extract the substring "gram" using slicing. How would you retrieve the string "World" from s = "Hello, World!" ? 3. Indexing and Slicing Combined: In the string s = "Data Science" , use slicing to get the word "Data" and indexing to get the first letter of "Science". 4. Negative Indexing and Slicing: Given s = "OpenAI" , use negative indexing to get the character 'I'. Using the same string s = "OpenAI" , extract the substring "pen" using negative slicing. 5. Advanced Slicing: How can you reverse the string s = "Python" using slicing? Given the string s = "123456789" , use slicing to get every second character starting from the second character. Answers to Practice Questions: 1. Indexing Practice: s results in 'W'. String : 2  The last character can be accessed with s[-1] , resulting in 'n'. 2. Slicing Practice: The substring "gram" can be extracted using s[3:7]. The string "World" can be retrieved with s[7:12]. 3. Indexing and Slicing Combined: s[:4] gives "Data", and s gives 'S'. 4. Negative Indexing and Slicing: s[-1] results in 'I'. The substring "pen" can be obtained with s[-5:-2]. 5. Advanced Slicing: Reverse the string with s[::-1] , resulting in "nohtyP". Every second character starting from the second can be extracted with s[1::2] , giving "2468". Complex Questions on Indexing and Slicing 1. Extract Alternating Characters and Reverse: Given the string s = "abcdefghijklm" , write a code snippet to: Extract every second character starting from the first character. Reverse the resulting substring. Answer: Extracting every second character: s[::2] results in "acegikm". Reversing the substring: s[::2][::-1] results in "mkgieca". 2. Nested Slicing: With s = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" , extract every third letter starting from the second letter and then reverse this result. String : 3  Answer: First, slice to get every third letter starting from the second: s[1::3] gives "BDFHJLNPRTXVZ". Then reverse: s[1::3][::-1] results in "ZVXTRPNLJHFD". 3. Manipulating Strings with Negative Indices: 4. For the string s = "PythonIsFun" , use slicing to: Extract the substring "Is". Replace "Is" with "Was" using slicing and concatenation. Answer: Extract "Is": s[6:8] results in "Is". Replace "Is" with "Was": s[:6] + "Was" + s[8:] results in "PythonWasFun". 5. Complex Slicing with Steps: Given s = "1234567890" , how can you: Extract the odd-indexed characters. Then reverse the extracted substring and extract every second character. Answer: Odd-indexed characters: s[1::2] results in "24680". Reverse and extract every second character: s[1::2][::-1][::2] results in "086". 6. Using Indexing and Slicing Together: For the string s = "WelcomeToPythonProgramming" , how can you: Extract "Python" and "Programming" separately. Then create a new string combining these two with a space in between. String : 4  Methods in string : 1. String Methods Case Conversion.lower() : Converts all characters to lowercase. pythonCopy code result = "Hello".lower() print(result) # Output: hello.upper() : Converts all characters to uppercase. pythonCopy code result = "Hello".upper() print(result) # Output: HELLO.capitalize() : Converts the first character to uppercase and the rest to lowercase. pythonCopy code result = "hello world".capitalize() print(result) # Output: Hello world.title() : Converts the first character of each word to uppercase. String : 5  pythonCopy code result = "hello world".title() print(result) # Output: Hello World.swapcase() : Swaps uppercase characters to lowercase and vice versa. pythonCopy code result = "Hello World".swapcase() print(result) # Output: hELLO wORLD String Checking.isalnum() : Returns True if all characters are alphanumeric. pythonCopy code result = "Hello123".isalnum() print(result) # Output: True.isalpha() : Returns True if all characters are alphabetic. pythonCopy code result = "Hello".isalpha() print(result) # Output: True.isdigit() : Returns True if all characters are digits. pythonCopy code result = "123".isdigit() print(result) # Output: True String : 6.islower() : Returns True if all characters are lowercase. pythonCopy code result = "hello".islower() print(result) # Output: True.isupper() : Returns True if all characters are uppercase. pythonCopy code result = "HELLO".isupper() print(result) # Output: True.isspace() : Returns True if all characters are whitespace. pythonCopy code result = " ".isspace() print(result) # Output: True String Manipulation.strip() : Removes leading and trailing whitespace. pythonCopy code result = " Hello ".strip() print(result) # Output: Hello.lstrip() : Removes leading whitespace. pythonCopy code result = " Hello ".lstrip() String : 7  print(result) # Output: Hello.rstrip() : Removes trailing whitespace. pythonCopy code result = " Hello ".rstrip() print(result) # Output: Hello.replace(old, new) : Replaces occurrences of a substring with another. pythonCopy code result = "Hello World".replace("World", "Python") print(result) # Output: Hello Python.split(separator) : Splits the string into a list using a specified separator. pythonCopy code result = "Hello World".split() print(result) # Output: ['Hello', 'World'].join(iterable) : Joins elements of an iterable into a string, using the string as a separator. pythonCopy code result = "-".join(["Hello", "World"]) print(result) # Output: Hello-World Searching.find(substring) : Returns the index of the first occurrence of the substring. String : 8  pythonCopy code result = "Hello World".find("World") print(result) # Output: 6.rfind(substring) : Returns the index of the last occurrence of the substring. pythonCopy code result = "Hello World World".rfind("World") print(result) # Output: 12.index(substring) : Similar to.find() , but raises a ValueError if the substring is not found. pythonCopy code result = "Hello World".index("World") print(result) # Output: 6.rindex(substring) : Similar to.rfind() , but raises a ValueError if the substring is not found. pythonCopy code result = "Hello World World".rindex("World") print(result) # Output: 12 Formatting.format(*args, **kwargs) : Formats the string using placeholders. pythonCopy code result = "Hello, {}!".format("World") String : 9  print(result) # Output: Hello, World! f-strings : A newer way to format strings, introduced in Python 3.6. pythonCopy code name = "World" result = f"Hello, {name}!" print(result) # Output: Hello, World! 2. Built-in Functions len() : Returns the length of the string. pythonCopy code result = len("Hello") print(result) # Output: 5 str() : Converts an object to a string. pythonCopy code result = str(123) print(result) # Output: '123' ord() : Returns the Unicode code point of a single character. pythonCopy code result = ord('A') print(result) # Output: 65 chr() : Returns the character corresponding to a Unicode code point. String : 10  pythonCopy code result = chr(65) print(result) # Output: 'A' String : 11