Section 1.1: Basic Example of a For Loop

Let's create a brief Python script named friends.py:

# The lines beginning with # are comments that Python ignores.

# file name: friends.py

friends = ['Elliot', 'Angela', 'Tyrell']

print(friends[0])

print(friends[1])

print(friends[2])

When we execute this code, it will display each name in the friends list:

$ python3 friends.py

Elliot

Angela

Tyrell

While this example only contains three names and is manageable, imagine handling a list with hundreds of entries. Here, a for loop becomes invaluable, allowing us to streamline our code. Let's revise the earlier code using a for loop:

# file name: friends.py

friends = ['Elliot', 'Angela', 'Tyrell']

for friend in friends:

print(friend)

In this case, the line for friend in friends: iterates through the friends list, assigning each element to the variable friend. Python then prints the value associated with friend and continues this process for every item in the list. You can think of this as, "For each friend in the list, print their name."

Section 1.2: Understanding Variable Naming

As we start our for loop, a new variable called friend is introduced, but it could be named anything you prefer:

# file name: friends.py

friends = ['Elliot', 'Angela', 'Tyrell']

for anything in friends:

print(anything)

Running the code again yields the same result:

$ python3 friends.py

Elliot

Angela

Tyrell

However, it's clear that using a descriptive variable name like friend is more intuitive given the context. While Python doesn't mind the name, clarity is beneficial for us as programmers.

Section 1.3: Delving Deeper into For Loops

For those who are new to coding, let’s examine the for loop more closely. Starting from the line:

for friend in friends:

Python retrieves the first entry from the friends list, which is "Elliot", and assigns it to the variable friend. The next line:

print(friend)

prints the current value of friend, which is "Elliot." Subsequently, Python returns to the start of the loop and retrieves the next item, "Angela," associating it with friend and printing it in the same manner. This process continues until all elements are processed.

As you become comfortable with for loops, you can create more complex scripts using concepts learned in previous lessons:

# file name: friends.py

friends = ['Elliot', 'Angela', 'Tyrell']

for friend in friends:

print(f"Bon Soir, {friend}!")

print(f"See you later, {friend}.n")

Running this code will yield:

$ python3 friends.py

Bon Soir, Elliot!

See you later, Elliot.

Bon Soir, Angela!

See you later, Angela.

Bon Soir, Tyrell!

See you later, Tyrell.

Thank you, everyone!

Lastly, in the above code, indentation is not merely a stylistic choice; it is crucial in Python, as shown here:

for friend in friends:

print(friend)

Proper indentation helps Python interpret the structure of your code. Errors in indentation are common, such as mistakenly indenting lines that don’t require it or neglecting to indent those that do. Familiarizing yourself with these potential pitfalls now will aid in preventing them later in your programming journey.