Iteration

• Definition: a repetition of a process

• used for an indefinite number of iterations

• Loops are control structures for codeblock iteration

• Repeatedly execute codeblack when the expression is True

• Boolean expression determines the execution of a codeblock

Iterating through an Iterable

• Iterable
  • An object that can be iterated or repeatedly applied
  • All sequences and containers are iterable
  • Has items that can be accessed.

Iterable For Loops in list - Example

# Define a list of numbers
numbers = [1, 2, 3, 4, 5]

# Iterate over each element in the list using a for loop
for num in numbers:
    print(num)

'''
for item in my_list:
    print(item)
'''

Example using a for loop to repeat an action

for i in range(5):
    print("Hello, world!")

Example using break to exit a loop early

for number in range(10):
    if number == 5:
        break
    print(number)

Iterable While Loops in list - Example

mylist = ['a','b','c']
# iterable mylist
i=0
# called index number

while i < len(mylist):
    ch = mylist[i]
    print(ch)
    i = i+1

Example using while loop to repeat until condition is false

count = 0
while count < 5:
    print(count)
    count += 1

Iteration with Dictionaries

• can be done over keys or key-value pairs using for loops and items() method
• Dictionary comprehension is used to create a new dictionary based on existing key-value pairs.

# Iterating over a dictionary
my_dict = {'a': 1, 'b': 2, 'c': 3}

# Iterating over keys
print("\nIterating over keys in a dictionary:")
for key in my_dict:
    print(key)

# Iterating over key-value pairs
print("\nIterating over key-value pairs in a dictionary:")
for key, value in my_dict.items():
    print(f"Key: {key}, Value: {value}")

# Using dictionary comprehension
print("\nCreating a new dictionary with comprehension:")
double_dict = {key: value * 2 for key, value in my_dict.items()}
print(double_dict)

Iteration with Tuples

• Tuples are iterated over similarly to lists, using a for loop. Tuple unpacking (enumerate function) can provide both index and value during iteration. Unlike lists and dictionaries, tuples do not support direct comprehension, but you can use a generator expression to achieve a similar effect.

# Iterating over a tuple
my_tuple = (1, 2, 3, 4, 5)

# Using a for loop
print("\nIterating over a tuple:")
for item in my_tuple:
    print(item)

# Using tuple unpacking
print("\nIterating over a tuple with unpacking:")
for i, item in enumerate(my_tuple):
    print(f"Index: {i}, Value: {item}")

# Using tuple comprehension 
# (not directly available, but you can use generator expression)
print("\nCreating a new tuple with generator expression:")
squared_tuple = tuple(x**2 for x in my_tuple)
print(squared_tuple)