Lists & loops
Iterate, transform, and combine sequences with readable loop patterns.
How to Summarize a List of Numbers in Python
Loop over a list of numbers to compute total, count, average, min, and max, then return them in a dictionary.
def summarize_numbers(numbers):
"""Return a dict with basic stats for a list of numbers."""
total = 0
count = 0
smallest = numbers[0]
largest = numbers[0]
for num in numbers:
total += num
count += 1
if num < smallest:
smallest = num
if num > largest:…How to Transpose a Matrix in Python (List of Lists)
Swap rows and columns of a 2D list using nested loops to produce a transposed matrix.
def transpose(matrix):
# Number of rows and columns in the original matrix
rows = len(matrix)
cols = len(matrix[0]) if rows > 0 else 0
# Create a new matrix with dimensions swapped
result = []
for j in range(cols):
new_row = []
for i in range(rows):
new_row.appe…How to Validate List Data in Python
A beginner-friendly validation helper that checks if data is a list, enforces minimum length, and optionally verifies item types with clear error messages.
def validate_data(data, expected_types=None, min_length=1):
"""Validate that data is a non-empty list and optionally check item types."""
if not isinstance(data, list):
return False, f"Expected a list, got {type(data).__name__}"
if len(data) < min_length:
return False, f"List must have…How to Validate Text Against Forbidden Words in Python
Checks whether a given text contains any forbidden words and returns a tuple with validity and offending words.
def validate_text(text, forbidden_words):
"""
Checks that text does not contain any forbidden words.
Returns (is_valid, offending_words) tuple.
"""
words = text.lower().split()
found = [word for word in words if word in forbidden_words]
return len(found) == 0, found
if __name__ == "__main…How to check list items by type and emptiness in Python
Loop through a list with enumerate(), classify each item as empty, number, or text, and print a formatted status for each element.
def check_data(data):
"""Check each item in a list and print whether it's valid."""
for i, item in enumerate(data):
if item is None or item == "":
status = "empty"
elif isinstance(item, (int, float)):
status = "number"
else:
status = "text"
pr…How to summarize and transform lists in Python
Compute count, sum, min, max, and average for a list and multiply each element by a factor using simple loops and built-in functions.
def summarize(data):
"""Return a summary of a list: count, sum, min, max, average."""
count = len(data)
total = sum(data)
minimum = min(data)
maximum = max(data)
average = total / count if count else 0
return count, total, minimum, maximum, average
def multiply_elements(data, factor=2):
…How to unzip a list of pairs into two lists in Python
Split a list of (a, b) tuples into two separate lists by iterating with a for loop and appending each element to its own output list.
def unzip(pairs):
"""Split a list of (a, b) pairs into two separate lists."""
if not pairs:
return [], []
firsts = []
seconds = []
for a, b in pairs:
firsts.append(a)
seconds.append(b)
return firsts, seconds
if __name__ == "__main__":
pairs = [(1, 'a'), (…Pairwise Adjacent Differences in a Python List
Computes the absolute differences between each pair of adjacent elements in a list using a concise list comprehension.
def adjacent_differences(nums):
"""Return list of absolute differences between adjacent elements."""
return [abs(nums[i] - nums[i + 1]) for i in range(len(nums) - 1)]
if __name__ == "__main__":
sample = [3, 7, 2, 9, 5]
diffs = adjacent_differences(sample)
print("Original list:", sample)
print…Round Robin Merge Multiple Lists in Python
Merge multiple lists by taking one element from each in turn, stopping when all lists are exhausted.
from itertools import cycle
def round_robin_merge(*lists):
"""Merge multiple lists by taking one element from each in turn."""
result = []
max_len = max(len(lst) for lst in lists)
for i in range(max_len):
for lst in lists:
if i < len(lst):
result.append(lst[i])…Separate Evens and Odds into Two Lists in Python
Split a list of numbers into two lists containing even and odd numbers using a simple loop and the modulo operator.
def separate_evens_odds(numbers):
evens = []
odds = []
for num in numbers:
if num % 2 == 0:
evens.append(num)
else:
odds.append(num)
return evens, odds
if __name__ == "__main__":
nums = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
evens, odds = separate_evens_odds(nu…Browse by section
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Lists & loops — Python code examples
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