Lists & loops
Iterate, transform, and combine sequences with readable loop patterns.
Enumerate a Python List with a Custom Start Index
Iterate over a list with an index that starts at a custom value (like 5) using Python's built-in enumerate() function with the start parameter.
fruits = ["apple", "banana", "cherry", "date"]
for index, fruit in enumerate(fruits, start=5):
print(f"{index}: {fruit}")Find All Occurrences of an Item in a Python List
Loop through a list with enumerate() to collect the index of every match for a target value.
def find_all(data, target):
"""Return indices of every occurrence of target in a list."""
indices = []
for index, item in enumerate(data):
if item == target:
indices.append(index)
return indices
if __name__ == "__main__":
sample = [10, 20, 30, 20, 40, 20, 50]
target_value …How to Calculate a Cumulative Sum in Python
Build a new list where each element equals the running total of all numbers up to that index in the original list.
numbers = [1, 2, 3, 4, 5]
cumulative_sum = []
running_total = 0
for num in numbers:
running_total += num
cumulative_sum.append(running_total)
print(cumulative_sum)How to Find the Third Smallest Element in a Python List
Find the third smallest distinct value in a Python list by sorting unique elements and returning the third index.
def find_third_smallest(numbers):
if len(numbers) < 3:
return None
unique_sorted = sorted(set(numbers))
if len(unique_sorted) < 3:
return None
return unique_sorted[2]
if __name__ == "__main__":
sample = [5, 2, 8, 2, 9, 1, 7, 3]
result = find_third_smallest(sampl…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 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)Browse by section
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Lists & loops — Python code examples
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