Lists & loops
Iterate, transform, and combine sequences with readable loop patterns.
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 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…Browse by section
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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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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.