Filtering and Transforming

Filter by Threshold

Walk a list and keep only the values that meet a condition — here, readings at or above a threshold. The replay shows kept growing with each qualifying element and staying flat when a value is rejected.

By hand

The Pythonic way

A list comprehension [v for v in values if v >= threshold] expresses the same filter in one line, without an explicit accumulator or append call.

naive.py 
values = [3, 7, 1, 9, 4, 8, 2, 6]
threshold = 5
kept = []
for v in values:
    if v >= threshold:
        kept.append(v)
print('RESULT:', kept)
library.py 
values = [3, 7, 1, 9, 4, 8, 2, 6]
threshold = 5
kept = [v for v in values if v >= threshold]
print('RESULT:', kept)

RESULT: [7, 9, 8, 6]

Implementation notes

  • kept grows visibly in the replay: [] → [7] → [7, 9] → [7, 9, 8] → [7, 9, 8, 6]; the four rejected values produce zero-delta events.
  • Every if v >= threshold: event is zero-delta (condition evaluation changes no variables); the kept.append(v) event that follows marks a passing value.
  • The list comprehension runs its own internal loop, so v does not appear as a traced variable in the library half.