Week-5-2

Loop Counting Techniques

While Loop Counting

• Initialization: Start with i, e.g., initialized to 5, and decrement in each iteration.

• Execution: Continues until i equals 1, thus executing a total of 5 iterations.

For Loops

• General Structure: The syntax follows for variable in container, where the variable takes on each value in the specified container such as a list or tuple.

• Examples:

  • Iterating Through a List: A for loop can greet each person: for name in [Bill, Nicole, John], resulting in "Hi Bill", "Hi Nicole", and "Hi John" consecutively.

  • Iterating Through Dictionaries: When looping through a dictionary, the variable represents the keys, enabling actions based on key-value pairs. For example: for c in channels results in statements like "MTV is on channel 35" and "Fox is on channel 11" based on respective keys.

  • Iterating Through Strings: A for loop can be used to modify strings, such as appending underscores to characters in a string like "TAKE", to potentially produce an output of "T_A_K_E_".

  • Summation with For Loops: Begin with total = 0; then, using a loop like for day in revenue_list, sum values to compute the average by dividing total by the length of the revenue list after the loop completes.

  • Reversing Lists: Use the reversed() function, e.g., for name in reversed(names_list), to output names in reverse order.

  • Using Range Function: range() generates sequences based on specified parameters; for example, range(5) gives 0 to 4, while range(5, 0, -1) counts downwards from 5 to 1. This function is commonly used in loops to define the number of iterations.

Nested Loops

• A nested loop consists of one loop within another, often termed the outer and inner loops. For instance, to create combinations of letters, the outer loop can iterate over A-Z for letter1, while the inner loop iterates A-Z for letter2, resulting in combinations like AA, AB, AC, etc.

Loop Control Statements

• Break Statement: This statement terminates the loop immediately when encountered, useful in scenarios where a specific condition or result is necessary to exit early from the loop.

• Continue Statement: It skips the current iteration and proceeds to the next one without executing any further code in the current loop cycle.

• Loop Else Statement: This part of the syntax executes a block of code after a loop finishes normally (not via a break), providing a mechanism to run statements always after the loop completes.

Enumerate Function

• The enumerate() function allows both indexing and value retrieval from a container during iteration. For instance, using for index, value in enumerate([4, 8, 10]) would yield pairs such as (0, 4), (1, 8), and (2, 10), thereby enabling simultaneous access to both the index and corresponding value of the elements.