Lists & loops
Iterate, transform, and combine sequences with readable loop patterns.
Format Lists of Tuples into Numbered Lines in Python
This code loops through a list of (name, grade) tuples and formats each into a numbered line using enumerate and f-strings.
def format_students(students):
formatted = []
for i, student in enumerate(students, start=1):
name, grade = student
formatted.append(f"{i}. {name}: {grade}")
return "\n".join(formatted)
if __name__ == "__main__":
students = [
("Alice", 92),
("Bob", 85),
("Charl…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 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 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'), (…Browse by section
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Lists & loops — Python code examples
What you will find here
This page collects lists & loops snippets — short, copy-ready Python you can paste into our free online IDE and run without installing anything. Each sample includes a plain-English explanation and the full source code.
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Samples are quick reference — one concept per page. For step-by-step teaching, use our Python tutorials. To test yourself, try quizzes or coding challenges. Clean up style with the Python formatter.