Python Tutorial

Python Loop Lists

Loop through a list with for, while, or list comprehension.

← Remove List Items List Comprehension →

for Loop

Print each item.

thislist = ["apple", "banana", "cherry"]
for x in thislist:
    print(x)

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

while Loop

Use an index and increment it until you reach len(list).

thislist = ["apple", "banana", "cherry"]
i = 0
while i < len(thislist):
    print(thislist[i])
    i += 1

📘 Real-World Deep Dive

The <code>for</code> loop is the workhorse for iterating lists — with the right idiom (<code>enumerate</code>, parallel iteration, comprehension form) you save boilerplate and avoid off-by-one bugs.

Real-Life Scenario

Walk two parallel lists of timestamps and prices, build a tidy table including a running average — without index arithmetic.

Real-Life Example

import csv, io

timestamps = ["09:00", "10:00", "11:00", "12:00", "13:00"]
prices     = [101.5, 102.7, 100.9,  99.4, 100.0]

print(f"{'time':<6} {'price':>8}  {'avg_so_far':>10}")
running_sum = 0.0
for i, (ts, px) in enumerate(zip(timestamps, prices), start=1):
    running_sum += px
    avg = running_sum / i
    print(f"{ts:<6} {px:>8.2f}  {avg:>10.2f}")

# Comprehension form for the table:
rows = [(ts, px, sum(prices[:i+1]) / (i + 1)) for i, (ts, px) in enumerate(zip(timestamps, prices))]
print("rows:", rows)

Expected Output

time    price  avg_so_far
09:00   101.50      101.50
10:00   102.70      102.10
11:00   100.90      101.70
12:00    99.40      101.13
13:00   100.00      101.04
rows: [('09:00', 101.5, 101.5), ..., ('13:00', 100.0, 101.04)]

Common mistakes

Building the running-avg with sum(prices[:i+1]) is O(n²); prefer a running accumulator.
range(len(xs)) is rarely what you want — use enumerate(xs) instead.
Tuples unpacked in for ... in have to match exactly; one too few or too many raises ValueError.

🚀 Performance & Best Practices

enumerate(start=1) lets you write i+1-less windowed computations.
itertools.tee + islice for sliding windows; avoid per-iteration slicing on big lists.
Comprehensions beat for+append for the same task — both in clarity and speed.

🧪 Try It Yourself

Write pair_diff(xs, ys) that returns the elementwise difference of two zipped lists.
Replace the running-sum example with a itertools.accumulate one-liner.
Benchmark a for loop against a comprehension for this example.

FAQ: Python Loop Lists

Common questions about this page.

What is Python Loop Lists?

Python Loop Lists is a Python Tutorial lesson that explains loop through list python in Python. Loop through a list with for, while, or list comprehension. Copy the samples and run them in the Python editor. It is written for beginners who want a clear definition and working examples.

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What is the syntax of loop through list python?

This Python Loop Lists tutorial shows loop through list python syntax with short Python examples. Use the code blocks in this lesson for the exact statements, then try them in your editor.

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What are common mistakes with loop through list python?

Common loop through list python mistakes include wrong syntax, mixing types, and skipping practice. Work through this Python Tutorial chapter in order, run every example, and check the output before moving on.

Why should I learn loop through list python?

Python Loop Lists is used in real Python work. Learning loop through list python helps you write clearer programs and continue the Python Tutorial tutorial on StudyGrid.

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Yes. You can learn loop through list python free on StudyGrid (studygrid.in). This chapter is part of the Python Tutorial path and includes examples, syntax, and next-step links.