strace.py

import fileinput
from datetime import datetime
import itertools as itl

def nwise(iterable, n=2):
  iters = itl.tee(iterable, n)
  for i, it in enumerate(iters):
    next(itl.islice(it, i, i), None)
  return zip(*iters)

first_time = None
fmt = '%H:%M:%S.%f'

for curr, nxt in nwise(fileinput.input(), 2):
  # print(f'curr: {curr}')
  # print(f'next: {nxt}')
  try:
    curr_time = datetime.strptime(curr.split()[0], fmt)
    next_time = datetime.strptime(nxt.split()[0], fmt)
    if not first_time:
      first_time = curr_time
      prev_str_time = first_time
    diff_since_start = curr_time - first_time
    this_cmd_duration = next_time - curr_time
    print(f'{round(diff_since_start.total_seconds() * 1000, 3):.3f} / {round(this_cmd_duration.total_seconds() * 1000, 3):.3f} ms: {curr}', end='')
  except:
    print(f'{curr}', end='')