I see this all the time when I'm reviewing code from developers transitioning to Python from languages like C++ or Java: they treat the for loop as a glorified counter. They spend so much time worrying about the index—the i variable—that they forget the actual data they're trying to work with.

Stop using range(len()) to access list items

Here is a classic example of the "counter" mindset. Let's say you have a list of user email addresses and you want to print each one. A lot of learners write it like this:

emails = ["alice@example.com", "bob@example.com", "charlie@example.com"]

for i in range(len(emails)):
    print(emails[i])

Technically, this works. But in Python, this is considered an "anti-pattern." You're creating a range of numbers, then using those numbers to look up an item in a list. It's verbose, it's slower, and it's exactly how we did things in 1995. You're adding an extra layer of mental overhead by tracking the index when you don't actually care about the number; you only care about the email.

Thinking of "for" as "for each"

In Python, the for loop is actually a "for-each" loop. It doesn't count; it iterates. It reaches into the collection and hands you the actual object, one by one.

emails = ["alice@example.com", "bob@example.com", "charlie@example.com"]

for email in emails:
    print(email)

See the difference? email isn't a number; it's the actual string. This makes your code read like a sentence in English. I've always found that the more your code looks like a sentence, the fewer bugs you'll introduce because the logic becomes obvious.

Handling the "But I actually need the index!" problem

Now, I know what you're thinking: "What if I need to know the position of the item? What if I need to print 'User 1: alice@example.com'?"

You still shouldn't go back to range(len()). Instead, use enumerate(). This is a built-in function that gives you both the index and the item at the same time. It's the professional way to handle this scenario.

emails = ["alice@example.com", "bob@example.com", "charlie@example.com"]

for index, email in enumerate(emails, start=1):
    print(f"User {index}: {email}")

Note that I used start=1. By default, Python starts counting at 0, but enumerate lets you shift that starting point so your output makes sense to humans.

Fine-tuning the flow with break and continue

Iteration isn't always a straight line from start to finish. Sometimes you need to bail out early or skip a specific item. That's where break and continue come in.

• break: Stops the loop entirely. Use this when you've found what you're looking for and there's no point in checking the rest of the list.
• continue: Skips the rest of the current block and jumps straight to the next item in the list.

Imagine you're searching for a specific "blacklisted" email in a list. You don't want to keep looking once you find it, and you want to skip over any empty strings in your data:

emails = ["alice@example.com", "", "malicious@spam.com", "bob@example.com"]
blacklist = "malicious@spam.com"

for email in emails:
    if not email: 
        continue  # Skip empty strings
    
    if email == blacklist:
        print("Security alert: Blacklisted email found!")
        break  # Stop searching immediately

Using continue keeps your code from becoming a giant mess of nested if statements, keeping the "happy path" of your logic aligned to the left margin of your editor.

📋 Practical Task

Filtering an Atmospheric Sensor Data Log

You have been given a list of temperature readings from a remote sensor. However, the sensor is glitchy: it occasionally records None values when it loses power, and it sometimes records "Impossible" readings (anything above 100°C or below -50°C) that should be ignored.

Your Task: Write a script that iterates through the sensor_readings list and calculates the average of the valid readings only.

Requirements:

• Use a for loop to iterate through the list.
• Use continue to skip None values and readings outside the valid range (-50 to 100).
• Keep a running total of the valid temperatures and a count of how many valid readings were found.
• Print the final average.

sensor_readings = [22.5, 23.1, None, 105.2, 21.8, -60.0, None, 24.0, 22.9]