Day 4 - Randomisation and Python Lists

Random Module

The random module in Python is used to generate

random numbers or make random selections.

It is widely used for games, testing, and other

applications where randomization is needed.

Common Functions in the random Module

1.random()

Generates a random floating-point number between 0.0 (inclusive) and 1.0 (exclusive).

Example:

   import random
   print(random.random())

Output

0.483475829

2. randint(a, b)

Generates a random integer between a and b (both inclusive).

Example:

print(random.randint(1, 10))

Output

Random number between 1 and 10

3.uniform(a, b)

Generates a random floating-point number between a and b.

Example

print(random.uniform(1.5, 5.5))

Output

Random float between 1.5 and 5.5

Use Cases

. Games: Randomizing player turns or shuffling cards.

. Testing: Generating test data.

Important Note

The numbers generated by the random module are pseudo-random, meaning they are determined by an algorithm and are not truly random.

Understanding Offsets and Appending Items to the Lists

Understanding Offset (Index) in Lists

In Python, a list is an ordered collection of items, and each item has a position called an index or offset. The index starts at 0 for the first item in the list and increments by 1 for each item.

Key Points:

1. Indexing starts at 0:

   • First item: Index 0

   • Second item: Index 1

   • Last item: Index -1 (negative indexing)

2. Accessing items using an offset:

   • You can retrieve an item by specifying its index within square brackets ([]).

   • Example:

       fruits = ['apple', 'banana', 'cherry']
       print(fruits[0])  #Output: apple
       print(fruits[1])  #Output: banana
       print(fruits[-1]) #Output: cherry (last item)
     

3. Out of range:

Accessing an index that doesn’t exist in the list raises an IndexError.

Example:

    (fruits[5])  # Raises IndexError

Appending Items to Lists

In Python, appending items to a list means adding new elements to the end of an existing list. Python lists are dynamic, so you can easily modify their size by adding items.

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How to Append Items to Lists

1. Using the append() Method

   The append() method adds a single item to the end of a list.

   It does not create a new list; it modifies the original list in place.

Example:

    numbers = [1, 2, 3]
    numbers.append(4)  # Adds 4 to the end of the list
    print(numbers)  # Output: [1, 2, 3, 4]

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2. Appending a List as an Item

   • You can append an entire list as a single item. In this case, the appended list becomes a nested list.

Example:

    numbers = [1, 2, 3]
    numbers.append([4, 5])  # Adds a nested list
    print(numbers)  # Output: [1, 2, 3, [4, 5]]

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3. Appending Items from Another Iterable

   Use the extend() method if you want to append multiple items from another iterable (like a list) to the current list.

   This adds the items individually, not as a nested list.

Example:

    fruits = ['apple', 'banana']
    fruits.extend(['cherry', 'orange'])  # Adds multiple items
    print(fruits)  # Output: ['apple', 'banana', 'cherry', 'orange']

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1. Key Differences: append() vs extend()

   | Operation | Effect | Example | Result | | --- | --- | --- | --- | | append(item) | Adds item as a single element | list.append([4, 5]) | [1, 2, 3, [4, 5]] | | extend(iterable) | Adds each element from iterable | list.extend([4, 5]) | [1, 2, 3, 4, 5] |

When to Use append()

• When adding one item at a time.

• When you want to add a nested list.

When to Use extend()

• When adding multiple items from another iterable.

• When you want to merge lists.

By understanding these methods, you can effectively grow and manipulate Python lists to suit your program's needs.

IndexErrors and Working with Nested Lists

IndexErrors in Python

An IndexError occurs in Python when you try to access an element of a sequence

(such as a list, tuple, or string) using an index that is out of range.

This means the index is either greater than the last index of the sequence or

3. less than the negative of the sequence's length.

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   What Causes IndexErrors?

   1. Accessing an Index Greater Than the Sequence Length:

      • If you try to access an index that is beyond the valid range, Python raises an IndexError.

        my_list = [1, 2, 3]
        print(my_list[3])  # IndexError: list index out of range

2. Using Negative Indices That Exceed the Range:

   • Negative indices count from the end of a sequence. If the negative index exceeds the sequence's length, an IndexError occurs.

        my_list = [1, 2, 3]
        print(my_list[-4])  # IndexError: list index out of range

3. Accessing an Empty Sequence:

   • An empty sequence (like an empty list) has no valid sequence.

        empty_list = []
        print(empty_list[0])  # IndexError: list index out of range

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How to Avoid IndexErrors

Check the Length of the Sequence Before Accessing: Use the len() function to ensure the index is within the valid range.

1.  my_list = [1, 2, 3]
    index = 3
    if index < len(my_list):
        print(my_list[index])
    else:
        print("Index out of range!")
   

Examples of IndexErrors

Example 1: Accessing an Invalid Index

    fruits = ["apple", "banana", "cherry"]
    print(fruits[5])  # IndexError: list index out of range

Example 2: Negative Index Exceeding Range

    numbers = [10, 20, 30]
    print(numbers[-4])  # IndexError: list index out of range

Example 3: Empty List

    empty_list = []
    print(empty_list[0])  # IndexError: list index out of range

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Key Takeaways

• Always ensure indices are within the sequence's valid range.

• Handle user inputs, dynamic indices, or uncertain data carefully to avoid unexpected errors.

• Use tools like len() and loops to work safely with sequences.

• Where My Learning Takes Me Next

  On Day 3 of the 100 Days of Python, I will learn about Python Loops.