Remove the first N items that match a condition in a Python list

Question

If I have a function matchCondition(x), how can I remove the first n items in a Python list that match that condition?

One solution is to itera

Answer 1

Starting Python 3.8, and the introduction of assignment expressions (PEP 572) (:= operator), we can use and increment a variable within a list comprehension:

# items = [1, 10, 2, 9, 3, 8, 4, 7]
total = 0
[x for x in items if not (x < 5 and (total := total + 1) <= 3)]
# [10, 9, 8, 4, 7]

This:

• Initializes a variable total to 0 which will symbolize the number of previously matched occurrences within the list comprehension
• Checks for each item if it both:
  • matches the exclusion condition (x < 5)
  • and if we've not already discarded more than the number of items we wanted to filter out by:
    • incrementing total (total := total + 1) via an assignment expression
    • and at the same time comparing the new value of total to the max number of items to discard (3)