Stanford CS106A - Programming Methodology (Python) Flashcards

Question 1

What is the primary purpose of `print()` and `input()` in Python?

Accepted Answer

`print()` is used to display output to the console, while `input()` is used to get user input from the console, typically as a string.

Question 2

Explain the difference between mutable and immutable data types in Python. Provide examples.

Accepted Answer

Mutable types can be changed after creation (e.g., `list`, `dict`, `set`). Immutable types cannot be changed after creation; any 'modification' creates a new object (e.g., `int`, `float`, `str`, `tuple`).

Question 3

How do you define a function in Python, and what is the significance of the `return` statement?

Accepted Answer

Functions are defined using the `def` keyword, followed by the function name, parameters in parentheses, and a colon. The `return` statement sends a value back to the caller and exits the function. If omitted, the function implicitly returns `None`.

Question 4

Describe the basic structure of an `if-elif-else` statement in Python.

Accepted Answer

An `if-elif-else` statement allows conditional execution based on boolean conditions.
```python
if condition1:
    # code if condition1 is true
elif condition2:
    # code if condition1 is false and condition2 is true
else:
    # code if all conditions are false
```

Question 5

What is a `for` loop used for in Python? Provide an example iterating over a list.

Accepted Answer

A `for` loop is used to iterate over a sequence (like a list, tuple, string, or range) or other iterable objects.
```python
my_list = [10, 20, 30]
for item in my_list:
    print(item)
```

Question 6

When would you use a `while` loop instead of a `for` loop?

Accepted Answer

A `while` loop is used when the number of iterations is not known beforehand and depends on a condition remaining true. A `for` loop is typically used when iterating over a known sequence or a fixed number of times.

Question 7

How do you access elements in a Python list? What is slicing?

Accepted Answer

Elements are accessed by their zero-based index (e.g., `my_list[0]`). Slicing allows accessing a sub-sequence of a list using `my_list[start:end:step]`, creating a new list.

Question 8

Explain the purpose of a Python dictionary. How do you add or access elements?

Accepted Answer

A dictionary is an unordered collection of key-value pairs, where each key must be unique and immutable. It's optimized for fast lookups.
```python
my_dict = {"name": "Alice", "age": 30}
# Access
print(my_dict["name"]) # Output: Alice
# Add/Modify
my_dict["city"] = "New York"
```

Question 9

What is the difference between a class and an object in Object-Oriented Programming (OOP)?

Accepted Answer

A `class` is a blueprint or template for creating objects, defining their attributes (data) and methods (behavior). An `object` (or instance) is a concrete realization of a class, created based on the class's definition.

Question 10

What is the `__init__` method in a Python class used for?

Accepted Answer

The `__init__` method is a special method (constructor) that is automatically called when a new object (instance) of a class is created. It's used to initialize the object's attributes with initial values.

Question 11

Explain the role of the `self` parameter in Python class methods.

Accepted Answer

`self` is a convention (not a keyword) that refers to the instance of the class itself. It must be the first parameter of any instance method, allowing the method to access and modify the object's attributes and call other methods.

Question 12

Describe the concept of inheritance in OOP.

Accepted Answer

Inheritance is an OOP mechanism where a new class (subclass/derived class) can inherit attributes and methods from an existing class (superclass/base class). This promotes code reusability and establishes an 'is-a' relationship.

Question 13

What is an algorithm?

Accepted Answer

An algorithm is a step-by-step procedure or a set of rules for solving a specific problem or performing a computation. It must be finite, unambiguous, and effective.

Question 14

Describe the Linear Search algorithm. When is it appropriate to use?

Accepted Answer

Linear Search (or Sequential Search) checks each element in a list sequentially until the target element is found or the end of the list is reached. It's appropriate for small, unsorted lists or when the list is not frequently searched. Its worst-case time complexity is $O(n)$.

Question 15

Explain the Binary Search algorithm. What is its primary requirement?

Accepted Answer

Binary Search is an efficient algorithm for finding an item from a *sorted* list. It repeatedly divides the search interval in half. Its primary requirement is that the list *must be sorted*. Its time complexity is $O(\log n)$.

Question 16

What is problem decomposition in programming?

Accepted Answer

Problem decomposition is a problem-solving strategy where a complex problem is broken down into smaller, more manageable sub-problems. Solving these smaller problems individually and then combining their solutions leads to the solution of the original complex problem.

Question 17

How can you handle errors in Python using `try-except` blocks?

Accepted Answer

`try-except` blocks are used for exception handling. Code that might raise an error is placed in the `try` block. If an error (exception) occurs, the code in the corresponding `except` block is executed.
```python
try:
    result = 10 / 0
except ZeroDivisionError:
    print("Cannot divide by zero!")
```

Question 18

What is a docstring in Python, and why is it important?

Accepted Answer

A docstring is a string literal used to document a module, class, function, or method. It's enclosed in triple quotes (`"""Docstring goes here"""`) and provides a concise summary of the object's purpose, arguments, and return values. It's important for code readability, maintainability, and automatic documentation generation.

Question 19

How do you iterate through both the indices and values of a list simultaneously in Python?

Accepted Answer

You can use the `enumerate()` function, which returns pairs of (index, value) for each item in the iterable.
```python
my_list = ['apple', 'banana', 'cherry']
for index, value in enumerate(my_list):
    print(f"Index: {index}, Value: {value}")
```

Question 20

What is the purpose of the `break` and `continue` statements in loops?

Accepted Answer

`break` immediately terminates the loop it's inside, transferring control to the statement immediately following the loop. `continue` skips the rest of the current iteration of the loop and proceeds to the next iteration.

Question 21

Describe the concept of 'abstraction' in programming.

Accepted Answer

Abstraction is the process of hiding complex implementation details and showing only the essential features of an object or system. In Python, functions and classes are forms of abstraction, allowing users to interact with an interface without needing to know the underlying complexity.

Question 22

What is the difference between passing arguments by value and by reference in Python?

Accepted Answer

Python's argument passing mechanism is often described as 'pass by object reference' or 'pass by assignment'. For immutable objects (like `int`, `str`, `tuple`), changes inside the function don't affect the original variable outside. For mutable objects (like `list`, `dict`), the function receives a reference to the same object, so modifications *to the object itself* inside the function will be visible outside. Reassigning the parameter variable inside the function will not affect the original variable.

Stanford CS106A - Programming Methodology (Python)

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