❔ Interview Question

What is the difference between __str__ and __repr__ methods in Python classes, and when would you implementstr
__str__ returns a human-readable string representation of an object (e.g., via print(obj)), making it user-friendly for displayrepr__repr__ aims for a more detailed, unambiguous string that's ideally executable as code (like repr(obj)), useful for debugging—imstr __str__ for end-user outrepr__repr__ for developer tools or str __str__ is defined.

tags: #interview #python #magicmethods #classes

➡️ @DataScienceQ 🤎

In Python, you can unpack sequences using *, to work with a variable number of elements. The * can be placed anywhere and it will collect all the extra elements into a separate variable.

a, b, c = 10, 2, 3      # Standard unpacking

a, *b = 10, 2, 3        # b = [2, 3]

a, *b, c = 10, 2, 3, 4  # b = [2, 3]

*a, b, c = 10, 2, 3, 4  # a = [10, 2]

👉  @DataScience4

In Python, generators are memory-efficient iterables created with functions using yield instead of return, allowing lazy evaluation for large datasets or infinite sequences. They're ideal for advanced scenarios like streaming data or coroutines.

def fibonacci(n):
    a, b = 0, 1
    for _ in range(n):
        yield a
        a, b = b, a + b

# Usage: list(fibonacci(10)) -> [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]

🆘 @DataScience4

In Python, enhanced for loops with enumerate() provide both the index and value of items in an iterable, making it ideal for tasks needing positional awareness without manual counters. This is more Pythonic and efficient than using range(len()) for list traversals.

fruits = ['apple', 'banana', 'cherry']
for index, fruit in enumerate(fruits):
    print(f"{index}: {fruit}")

# Output:
# 0: apple
# 1: banana
# 2: cherry

# With start offset:
for index, fruit in enumerate(fruits, start=1):
    print(f"{index}: {fruit}")
# 1: apple
# 2: banana
# 3: cherry

#python #forloops #enumerate #bestpractices

✉️ @DataScience4

In Python, lists are versatile mutable sequences with built-in methods for adding, removing, searching, sorting, and more—covering all common scenarios like dynamic data manipulation, queues, or stacks. Below is a complete breakdown of all list methods, each with syntax, an example, and output, plus key built-in functions for comprehensive use.

📚 Adding Elements
⦁ append(x): Adds a single element to the end.

  lst = [1, 2]
  lst.append(3)
  print(lst)  # Output: [1, 2, 3]
  

⦁ extend(iterable): Adds all elements from an iterable to the end.

  lst = [1, 2]
  lst.extend([3, 4])
  print(lst)  # Output: [1, 2, 3, 4]
  

⦁ insert(i, x): Inserts x at index i (shifts elements right).

  lst = [1, 3]
  lst.insert(1, 2)
  print(lst)  # Output: [1, 2, 3]
  

📚 Removing Elements
⦁ remove(x): Removes the first occurrence of x (raises ValueError if not found).

  lst = [1, 2, 2]
  lst.remove(2)
  print(lst)  # Output: [1, 2]
  

⦁ pop(i=-1): Removes and returns the element at index i (default: last).

  lst = [1, 2, 3]
  item = lst.pop(1)
  print(item, lst)  # Output: 2 [1, 3]
  

⦁ clear(): Removes all elements.

  lst = [1, 2, 3]
  lst.clear()
  print(lst)  # Output: []
  

📚 Searching and Counting
⦁ count(x): Returns the number of occurrences of x.

  lst = [1, 2, 2, 3]
  print(lst.count(2))  # Output: 2
  

⦁ index(x[, start[, end]]): Returns the lowest index of x in the slice (raises ValueError if not found).

  lst = [1, 2, 3, 2]
  print(lst.index(2))  # Output: 1
  

📚 Ordering and Copying
⦁ sort(key=None, reverse=False): Sorts the list in place (ascending by default; stable sort).

  lst = [3, 1, 2]
  lst.sort()
  print(lst)  # Output: [1, 2, 3]
  

⦁ reverse(): Reverses the elements in place.

  lst = [1, 2, 3]
  lst.reverse()
  print(lst)  # Output: [3, 2, 1]
  

⦁ copy(): Returns a shallow copy of the list.

  lst = [1, 2]
  new_lst = lst.copy()
  print(new_lst)  # Output: [1, 2]
  

📚 Built-in Functions for Lists (Common Cases)
⦁ len(lst): Returns the number of elements.

  lst = [1, 2, 3]
  print(len(lst))  # Output: 3
  

⦁ min(lst): Returns the smallest element (raises ValueError if empty).

  lst = [3, 1, 2]
  print(min(lst))  # Output: 1
  

⦁ max(lst): Returns the largest element.

  lst = [3, 1, 2]
  print(max(lst))  # Output: 3
  

⦁ sum(lst[, start=0]): Sums the elements (start adds an offset).

  lst = [1, 2, 3]
  print(sum(lst))  # Output: 6
  

⦁ sorted(lst, key=None, reverse=False): Returns a new sorted list (non-destructive).

  lst = [3, 1, 2]
  print(sorted(lst))  # Output: [1, 2, 3]
  

These cover all standard operations (O(1) for append/pop from end, O(n) for most others). Use slicing lst[start:end:step] for advanced extraction, like lst[1:3] outputs ``.

#python #lists #datastructures #methods #examples #programming

⭐ @DataScience4