Lists & loops
Iterate, transform, and combine sequences with readable loop patterns.
Find Duplicate Elements in a Python List
Identifies and returns duplicate elements from a Python list using sets for efficient membership tests.
def find_duplicates(lst):
seen = set()
duplicates = set()
for item in lst:
if item in seen:
duplicates.add(item)
else:
seen.add(item)
return list(duplicates)
if __name__ == "__main__":
sample = [1, 2, 3, 2, 4, 1, 5, 3]
print(find_duplicates(sample))How to Get the Union of Two Lists Without Duplicates in Python
Merge two lists and remove duplicate values using a set, then convert back to a list.
def union_without_duplicates(list1, list2):
return list(set(list1 + list2))
if __name__ == "__main__":
list_a = [1, 2, 3, 4]
list_b = [3, 4, 5, 6]
result = union_without_duplicates(list_a, list_b)
print(f"Union of {list_a} and {list_b}: {result}")Intersection of Two Lists Preserving Order in Python
This code returns the common elements between two lists while preserving the order they appear in the first list, filtering out duplicates.
def intersection_preserving_order(list1, list2):
"""
Return the intersection of two lists while preserving the order
of elements as they appear in list1.
"""
set2 = set(list2)
result = []
seen = set()
for item in list1:
if item in set2 and item not in seen:
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Lists & loops — Python code examples
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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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