Lists & loops
Iterate, transform, and combine sequences with readable loop patterns.
How to Partition a List Around a Pivot in Python
This code splits a list into three parts—elements less than, equal to, and greater than a pivot—then concatenates them to produce a partitioned list while preserving the original order within each group.
def partition_list(lst, pivot):
less = []
equal = []
greater = []
for item in lst:
if item < pivot:
less.append(item)
elif item == pivot:
equal.append(item)
else:
greater.append(item)
return less + equal + greater
if __name__ == "__main__…How to Process Text Lines with Lists and Loops in Python
This code processes a list of text lines by stripping whitespace, converting to uppercase, and reporting character counts per line and totals.
def process_text(lines):
"""Convert a list of text lines to uppercase and report line statistics."""
processed = []
total_chars = 0
for index, line in enumerate(lines, start=1):
cleaned = line.strip().upper()
processed.append(cleaned)
total_chars += len(cleaned)
pri…How to Process Text into Words in Python
Splits a string into words, strips punctuation, and returns a list of uppercase words using a loop.
def convert_text_processor(text):
words = text.split()
processed = []
for word in words:
clean = word.strip('.,!?;:')
if len(clean) > 0:
processed.append(clean.upper())
return processed
if __name__ == "__main__":
sample_text = "Hello, world! This is a Python e…How to Process Text with Lists and Loops in Python
A beginner-friendly text processor that splits a sentence into words, filters by length, counts vowels, and reports results using lists and loops.
text = "Python makes text processing easy and fun"
words = text.lower().split()
print("Words in the sentence:")
for index, word in enumerate(words, start=1):
print(f"{index}. {word}")
filtered_words = [word for word in words if len(word) > 3]
print(f"\nWords longer than 3 characters: {filtered_words}")
letter…How to Process Text with Lists and Loops in Python
Iterate over a list of text lines to count words, show uppercase versions, and report character counts per line.
# text_processor.py
def process_text(lines):
"""Count words, show uppercase, and count characters per line."""
total_words = 0
print("Line-by-line analysis:")
for i, line in enumerate(lines, start=1):
words = line.split()
total_words += len(words)
print(f" Line {i}: {len(words…How to Reverse a List in Place Without Using reverse() in Python
A two-pointer while loop swaps elements from both ends toward the center to reverse a list in place without creating a copy.
def reverse_list_in_place(lst):
left = 0
right = len(lst) - 1
while left < right:
lst[left], lst[right] = lst[right], lst[left]
left += 1
right -= 1
if __name__ == "__main__":
my_list = [1, 2, 3, 4, 5]
print("Original:", my_list)
reverse_list_in_place(my_list)
prin…How to Rotate a List in Python
Rotate a list to the right by k positions using Python's list slicing and modulo arithmetic.
def rotate_list_right(lst, k):
if not lst:
return lst
k = k % len(lst)
return lst[-k:] + lst[:-k] if k != 0 else lst
if __name__ == "__main__":
sample = [1, 2, 3, 4, 5, 6, 7]
for k in [0, 1, 3, 8, 20]:
print(f"k={k}: {rotate_list_right(sample, k)}")How to Safely Convert a List of Strings to Integers in Python
Convert a list of strings to integers while skipping invalid entries and collecting the failed values for inspection.
def safe_to_int(values):
"""Safely convert a list of strings to integers, skipping invalid entries."""
result = []
errors = []
for value in values:
try:
result.append(int(value))
except (ValueError, TypeError):
errors.append(value)
return result, errors
if …How to Shuffle a List in Python
Shuffle a Python list in place or return a new shuffled copy using the random module.
import random
def shuffle_list(items):
shuffled = items[:]
random.shuffle(shuffled)
return shuffled
if __name__ == "__main__":
original = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
result = shuffle_list(original)
print(f"Original: {original}")
print(f"Shuffled: {result}")How to Sort a List in Python in Ascending and Descending Order
This code demonstrates three ways to sort a list in Python: returning a new sorted list with sorted(), reversing the sort order, and sorting a list in place with the list.sort() method.
def get_sorted_data(numbers):
"""Return a new list sorted in ascending order."""
return sorted(numbers)
def reverse_sort(data):
"""Return a new list sorted in descending order."""
return sorted(data, reverse=True)
def sort_in_place(data):
"""Sort the given list in place (modifies original)."""
…How to Sort a List of Dictionaries by a Key in Python
Sort a list of dictionaries by a specified key field, optionally in descending order, using Python's built-in sorted() function.
def sort_dicts_by_key(data, key, reverse=False):
return sorted(data, key=lambda item: item.get(key), reverse=reverse)
if __name__ == "__main__":
people = [
{"name": "Alice", "age": 30},
{"name": "Bob", "age": 25},
{"name": "Charlie", "age": 35},
]
sorted_by_age = sort_dicts_b…How to Sort a List of Tuples by the Second Element in Python
Sorts a list of tuples by the second element using the sorted() function with a lambda key, preserving the original list.
def sort_tuples_by_second(tuples_list):
"""Sort a list of tuples by the second element."""
return sorted(tuples_list, key=lambda x: x[1])
if __name__ == "__main__":
data = [(1, 5), (3, 2), (2, 8), (4, 1)]
sorted_data = sort_tuples_by_second(data)
print("Original list:", data)
print("Sorted by…How to Split a List at the First Occurrence of a Value in Python
This function splits a list into two parts at the first occurrence of a given value, returning the left and right portions.
def split_at_first(lst, value):
try:
idx = lst.index(value)
return lst[:idx], lst[idx:]
except ValueError:
return lst, []
if __name__ == "__main__":
sample = [1, 2, 3, 4, 3, 5]
value = 3
left, right = split_at_first(sample, value)
print("Left:", left)
print("Right:"…How to Split a List into Chunks in Python
Split a list into fixed-size sublists using a simple list comprehension with slicing.
def chunk_list(lst, size):
"""Split a list into sublists of given size."""
return [lst[i:i + size] for i in range(0, len(lst), size)]
if __name__ == "__main__":
sample = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
print(chunk_list(sample, 3))How to Standardize a List with Z-Score Normalization in Python
This code computes the z-score for each number in a list, standardizing the data to have zero mean and unit variance using the statistics module.
import statistics
def z_score_normalize(values):
"""Standardize a list of numbers using z-score normalization."""
if not values or len(values) < 2:
raise ValueError("Need at least 2 values for meaningful z-score normalization")
mean = statistics.mean(values)
std_dev = statistics.stdev(val…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 Swap Two Indices in a Python List
Swap two elements at given indices in a Python list using simultaneous assignment, then return the modified list.
def swap_indices(lst, i, j):
lst[i], lst[j] = lst[j], lst[i]
return lst
if __name__ == "__main__":
my_list = [10, 20, 30, 40, 50]
print("Original list:", my_list)
swapped = swap_indices(my_list, 1, 3)
print("After swapping indices 1 and 3:", swapped)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 Truncate a List to Max Length in Python (Keep Head)
This code returns a new list containing only the first max_length items from the original list, using Python's slice syntax.
from typing import List
def truncate_head(lst: List[object], max_length: int) -> List[object]:
"""Return a new list with at most max_length items from the head."""
if max_length < 0:
raise ValueError("max_length must be non-negative")
return lst[:max_length]
if __name__ == "__main__":
# Examp…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 Zip Two Lists into Pairs in Python
Combine two lists element-wise into a list of tuples using Python's built-in zip() function.
def zip_lists_into_pairs(list1, list2):
pairs = list(zip(list1, list2))
return pairs
if __name__ == "__main__":
fruits = ["apple", "banana", "cherry"]
quantities = [3, 5, 2]
result = zip_lists_into_pairs(fruits, quantities)
print(result)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 split a list by condition in Python
Splits a list into two lists based on a condition function, returning matched and unmatched items.
def split_by_condition(items, condition):
"""
Split a list into two lists based on a condition.
The first list contains items where condition(item) is True,
the second list contains the rest.
"""
matched = []
unmatched = []
for item in items:
if condition(item):
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Lists & loops — Python code examples
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