def trace(frame, event, arg):
  relevant_fname_substr = ''  # populate with filename substring
  try:
    if relevant_fname_substr not in frame.f_code.co_filename:
      return
    print("{0.f_code.co_filename}: {0.f_lineno}".format(frame))
  except Exception:
    pass
from contextlib import contextmanager
@contextmanager
def tracing(trace_fn=trace):
  import sys
  sys.settrace(trace_fn)
  try:
    yield
  finally:
    sys.settrace(None)