Python For Loops

Python for Loops

• A for loop iterates over a sequence (e.g., list, tuple, string, range).
• It executes a code block repeatedly for each item in the sequence.

Basic Syntax

• for keyword followed by a variable name.
• in keyword.
• The sequence to iterate over.
• Colon (:) to start the code block.
• Indentation for the code block.

Iterating over Lists

• Example iterating over a list of numbers:

numbers = [1, 2, 3, 4, 5]
for number in numbers:
    print(number)

• Prints each number on a new line.

Iterating over Strings

• Strings are iterable sequences.
• Access each character:

my_string = "hello"
for character in my_string:
    print(character)

Iterating with range()

• Loops a specific number of times.
• range(start, stop, step) creates a sequence of numbers. Defaults to range(0, stop, 1).
• Example looping 5 times:

for i in range(5):
   print(i)

• Example looping from 2 to 5 with a step of 2:

for i in range(2, 6, 2):
    print(i)

break Statement

• Terminates the loop prematurely.
• Used when a specific condition is met:

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

continue Statement

• Skips the rest of the code block in the current iteration, moving to the next.

for i in range(5):
    if i == 2:
        continue
    print(i)

Nested Loops

• Loops placed inside another loop.
• Inner loop completes all iterations per outer loop iteration.

rows = 2
cols = 3

for row in range(rows):
    for col in range(cols):
        print(f"({row},{col})")

else Clause (with loops)

• Executes a code block when the loop completes normally (without break).

for i in range(3):
    print(i)
else:
    print("Loop completed normally")

Looping over Dictionaries

• Dictionaries are iterable.
• Iteration by default is over the keys.

my_dict = {"a": 1, "b": 2, "c": 3}
for key in my_dict:
    print(key)

## Access values:
for key in my_dict:
    print(f"Key: {key}, Value: {my_dict[key]}")

Looping over enumerate

• enumerate() function provides both index and value of an iterable.

my_list = ["apple", "banana", "cherry"]
for index, item in enumerate(my_list):
    print(f"Index: {index}, Item: {item}")

Important Considerations

• Python's indentation is crucial.
• Ensure the sequence being iterated over is valid.
• Avoid infinite loops.
• Choose the correct loop type (e.g., for for sequences, while for conditions).