Generate (index, value) pairs where the 1‑based index is a multiple of 4.

Signals the intent to process every fourth item in a sequence, counting from one.

When you need to process items at regular intervals (e.g., every fourth log entry, sampling data at a fixed stride).

Data processing pipelines, batch processing, sampling intervals, iterating over records with a fixed stride.

(idx, val) for idx, val in enumerate(data, start=1) if idx % 4 == 0

(idx, val) for idx, val in enumerate(data, start=1) if idx % 4 == 0

data (iterable), start (int, default 1), divisor (int, default 4), tuple pattern (idx, val) can be changed to other destructuring.

• enumerate
• modulo
• filter
• list comprehension
• itertools.islice

• start value
• divisor
• tuple shape (e.g.
• just idx)
• using range instead of enumerate
• using slice notation.

Using start=0 (or omitting it) leads to 0‑based indices; forgetting the parentheses around the generator expression; confusing the modulo condition with slice step; misreading the 1‑based vs 0‑based offset.

List comprehension: [(i, v) for i, v in enumerate(data, 1) if i % 4 == 0]; itertools.islice(data, 3, None, 4) for a 0‑based slice; enumerate(data) if i % 4 == 3.

Confusing 0‑based versus 1‑based indexing; omitting start=1 selects indices 0,4,8…; misreading the modulo condition as a step size.

• enumeration‑filter patterns

Produces 1‑based indices that are multiples of four, effectively selecting the 4th, 8th, 12th, … elements of the original sequence.

Signals the developer’s intent to process items at regular intervals starting from the first element as count one.

Every fourth item, counting from one.

The start=1 argument makes the enumeration 1‑based; without it the indices would be 0‑based.

Consider using itertools.islice(data, 3, None, 4) for a slice‑based approach, or a list comprehension if a list is needed.