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Questions and Answers

What happens if a derived class method has the same name as a method from its parent class?

  • The derived class method overrides the parent class method. (correct)
  • The parent class method is called instead.
  • The derived class method is ignored.
  • Python raises a NameError.

    • What will be the output of the statement 'Echo' * 3?

  • 'Echo'
  • 'EchoEcho'
  • 'Echo 3'
  • 'EchoEchoEcho' (correct)

    • Which method is used to extract a substring from a string?

  • slice()
  • index()
  • slicing with [:] (correct)
  • substring()

    • How would you get the length of the string 'Python'?

    <p>len('Python')</p> Signup and view all the answers

    What does the split() function do when called on a string?

    <p>Breaks down the string into a list of substrings.</p> Signup and view all the answers

    What is the result of 'Hello World'.replace('World', 'Python')?

    <p>'Hello Python'</p> Signup and view all the answers

    Which of the following methods will make all characters in a string lowercase?

    <p>str.lower()</p> Signup and view all the answers

    What will ' '.join(['This', 'is', 'a', 'sentence.']) return?

    <p>'This is a sentence.'</p> Signup and view all the answers

    What is the primary difference between a for loop and a while loop?

    <p>For loops iterate over a sequence, while while loops depend on a condition.</p> Signup and view all the answers

    When should a while loop be preferred over a for loop?

    <p>When the number of iterations is unknown or based on a condition.</p> Signup and view all the answers

    What does the break statement do in a loop?

    <p>It exits the loop immediately, skipping any remaining iterations.</p> Signup and view all the answers

    What can result from poor management of a while loop?

    <p>It may lead to infinite loops or errors.</p> Signup and view all the answers

    How is an exception defined in programming?

    <p>An error detected during execution that may cause a program to crash.</p> Signup and view all the answers

    What happens when attempting to concatenate a string and an integer?

    <p>An exception will be raised indicating the types are incompatible.</p> Signup and view all the answers

    Why is implicit initialization advantageous in a for loop?

    <p>It simplifies the syntax and reduces potential errors.</p> Signup and view all the answers

    What is a common use case for a for loop?

    <p>Processing a fixed-length sequence or defined range.</p> Signup and view all the answers

    What does the slice text[0:6] return for the string 'PythonProgramming'?

    <p>Python</p> Signup and view all the answers

    How does using the step argument in slicing change the output of text[0:12:2]?

    <p>It returns every second character.</p> Signup and view all the answers

    What will the slice text[::-1] return for the string 'Python'?

    <p>nohtyP</p> Signup and view all the answers

    If text is 'Python' and you slice it as text[0:50], what is the output?

    <p>Python</p> Signup and view all the answers

    What is the outcome of slicing text[1:4] from 'Python'?

    <p>yth</p> Signup and view all the answers

    What statement in Python is used to handle exceptions?

    <p>try/except statement</p> Signup and view all the answers

    What can be inferred about the immutability of strings in Python with respect to slicing?

    <p>Slicing creates a new string without altering the original.</p> Signup and view all the answers

    In what scenario might string slicing be particularly useful?

    <p>Extracting substrings for manipulation.</p> Signup and view all the answers

    What does the 'try' block contain in an exception handling structure?

    <p>Statements that can potentially raise an exception</p> Signup and view all the answers

    Which mode is used to create a new file or overwrite an existing one in Python?

    <p>w</p> Signup and view all the answers

    What will the expression full_name[:4] evaluate to if full_name is 'John Doe'?

    <p>John</p> Signup and view all the answers

    When opening a file in Python, what does the 'r+' mode allow you to do?

    <p>Read and write, with the pointer at the beginning</p> Signup and view all the answers

    When an age input is not a positive integer, which error should be raised in the program?

    <p>ValueError</p> Signup and view all the answers

    What does the 'append' mode do when writing to a file?

    <p>It writes content at the end of an existing file.</p> Signup and view all the answers

    Which of the following is a correct way to open a file in Python for reading in binary format?

    <p>open('file.txt', 'rb')</p> Signup and view all the answers

    What is the primary purpose of an exception handler?

    <p>To ensure the program continues running after an exception occurs</p> Signup and view all the answers

    What does the append() method do when called on a list?

    <p>It modifies the list in place by adding the element to the end.</p> Signup and view all the answers

    What is a key characteristic of a lambda function?

    <p>It can only have one expression.</p> Signup and view all the answers

    When should you typically use a lambda function?

    <p>When a simple, short function is needed temporarily.</p> Signup and view all the answers

    How does the map() function work with a lambda function?

    <p>It applies a function to all items in an input list.</p> Signup and view all the answers

    What is the output of the following code: numbers = [1, 2, 3, 4]; squares = list(map(lambda x: x ** 2, numbers)); print(squares)?

    <p>[1, 4, 9, 16]</p> Signup and view all the answers

    What does the filter() function do when combined with a lambda function?

    <p>It filters elements based on a condition defined by the lambda function.</p> Signup and view all the answers

    What is the primary use of lambda functions with the sorted() function?

    <p>To sort elements based on specific keys or criteria.</p> Signup and view all the answers

    Given a list of dictionaries, how would you typically sort them using sorted() with a lambda function?

    <p>By using a lambda function to specify the key from each dictionary.</p> Signup and view all the answers

    What is the purpose of the base case in a recursive function?

    <p>To prevent infinite recursion</p> Signup and view all the answers

    In the LEGB rule, where do variables in an enclosing function get accessed?

    <p>Inside the enclosing and nested functions</p> Signup and view all the answers

    Which of the following is a direct consequence of lacking a base case in recursion?

    <p>The function will lead to a stack overflow error</p> Signup and view all the answers

    What does the 'Global Scope' refer to in the context of variable accessibility?

    <p>Variables defined at the top level of the script/module</p> Signup and view all the answers

    When calculating factorials using recursion, what is the recursive case for $n!$?

    <p>$n! = n imes (n-1)!$</p> Signup and view all the answers

    What kind of error is caused when a function calls itself indefinitely?

    <p>Stack Overflow Error</p> Signup and view all the answers

    What part of the LEGB rule corresponds to the built-in scope?

    <p>Functions and variables that are predefined in Python</p> Signup and view all the answers

    Which statement about recursion is inaccurate?

    <p>Every recursive function must have exactly two base cases.</p> Signup and view all the answers

    Study Notes

    Python Basics

    • Python is a dynamic language, meaning variable types are determined at runtime, offering flexibility in assigning various data types to variables.
    • It's strongly typed, enforcing strict type rules. Implicit conversions (e.g., combining strings and integers) are prevented, which may generate errors.
    • Control flow structures include conditional statements (e.g., if, elif, else) and loops (e.g., for, while) for decision-making and repetitive operations respectively.
    • Python supports exception handling (try, except, finally) and control flow statements (break, continue, pass) for managing code execution within loops and blocks.

    Pass By Value vs. Returning a Value

    • In the first example, the function modifies a local copy of the variable, not the original, and hence output is 1.
    • In the second example, the function returns a value, and the variable will hold that returned value. In that case, the output is 2.

    Functions

    • set(): Creates a set from a sequence of elements, removing duplicates.
    • map(): Applies a function to each item in an iterable. (Often converted to a list)
    • split(): Splits a string into substrings(based on whitespace by default)
    • len(): Returns the number of elements in a collection.

    More Functions

    • sum(): Calculates the sum of all elements in a collection.
    • add(): Adds an element to a set; if the element exists, the set remains unchanged.

    More Functions (Continued)

    • discard(): Removes an element from a set if it exists; does nothing if the element doesn't exist.
    • The remove() method, unlike discard(), raises an error if the element is not present.

    append()

    • Adds an element to the end of a list.
    • Modifies the original list directly.
    • Doesn't return a new list.

    Lambda Functions

    • Lambda functions are small, anonymous functions.
    • Useful when a small function is needed temporarily.
    • Usually combined with functions like map(), filter(), and sorted().
    • Syntax: lambda arguments: expression

    Lambda and Built-in functions

    • In a map operation, lambda functions are applied to each item in a list to perform operations such as squaring each number.
    • The filter operation works with lambda functions to filter items from a list based on a provided condition such as getting only even numbers.
    • sorted uses lambda to sort items such as lists of tuples by a specific component.
    • Sorting a list of dictionaries can be done using the sorted function in conjunction with a lambda function.

    range()

    • Used in loops to iterate over a sequence of numbers, specifying the number of iterations or to access elements by index.
    • Syntaxes:
      • range(stop): Generates numbers from 0 to stop-1.
      • range(start, stop): Generates numbers from start to stop-1.
      • range(start, stop, step): Generates numbers from start to stop-1 with increments of step.

    Scope of Variables in Python

    • Python has four built-in scopes: Built-in, Global, Enclosing (Nonlocal), and Local (LEGB).
      • Variables within functions have local scope and are only accessible within the function itself.
    • Enclosing functions(nested functions) have access to variables in enclosing scope.
    • Global variables are declared outside functions and accessible throughout the entire program.

    Recursion

    • Recursion occurs when a function calls itself, directly or indirectly, as part of its execution,
    • Every recursive function needs a base case to stop the recursion and prevent infinite loops.
    • Recursive cases are where the function calls itself with a modified argument gradually moving toward the base case.

    Example: Factorial Calculation

    • Factorial of a non-negative integer n, denoted by n!, is the product of all positive integers less than or equal to n.
    • n! = n * (n-1) * (n-2)... * 1

    Example: factorial Function

    • This function calculates the factorial of a given non-negative number using recursion and the base case(n==1).

    Valid or Invalid Code Snippets

    • Demonstrates correct and incorrect ways to utilize Python features like classes, methods, and exception handling to avoid common errors and misunderstandings about them.

    String Methods

    • String concatenation (+) combines two strings into one.
    • String repetition (*) repeats strings multiple times
    • String slicing ([start:end]) fetches a substring
    • String splitting (.split()) breaks a string into a list of substrings.
    • String joining ('.join') joins list of strings into one string
    • String replacing (replace()) replaces a substring of another.

    String Methods(continued)

    • String case functions (lower(), upper(), capitalize(), title()): Modifies lowercase/uppercase characters.
    • Strip whitespace function (strip(), rstrip, lstrip): removes leading and trailing spaces/characters
    • String methods like find() are for searching for a substring within a string
    • in keyword: Checks for a string within another string
    • String formatting: Inserts variables into strings either by using .format or f-strings

    String Slicing Use Cases

    • Extract substrings from a given range of indices
    • Reverse a string
    • Handling out-of-bounds indices
    • Immutability in string slicing: Slicing creates a separate copy of strings

    Looping Statements (General Points)

    • Python offers two primary looping constructs: for and while.
    • Use for when the loop count is known, and use while when it's not.

    Exceptions (General Points)

    • Exceptions are errors that occur during program execution.
    • try...except blocks are used to handle potential exceptions gracefully, preventing crashes.

    File I/O (General Points)

    • The open() function is used to create a file object for reading, writing, or appending data to a file.
    • File handling modes like 'r' (read), 'w' (write), 'a' (append), 'r+' (read and write), etc are used when opening file.
    • The close() method is crucial to release the file resources.
    • Function like read(), readline(), readlines() can be used to read data from a file line by line

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