Select from 'left' file to resolve conflicts

select_left.py

def select_left(file):
  with open(file) as f:
    contents=f.read()

  lines = contents.split('\n')

  n_conflicts = sum([l.startswith('<<<<') for l in lines])

  keep=True
  outfile=[]

  for line in lines:
    if line.startswith('===='):
      keep=False
    elif line.startswith('>>>>'):
      keep=True
    elif keep and not line.startswith('<<<<'):
      outfile.append(line)

  conflicts_markers_remaining = sum([l.startswith('<<<<') or l.startswith('====') or l.startswith('>>>>') for l in outfile])
  if conflicts_markers_remaining:
    raise ValueError('Still {} conflict markers remaining!'.format(conflict_markers_remaining))

  print('Removed {} lines and {} conflicts'.format((len(lines) - len(outfile)), n_conflicts))

  with open(file, 'w') as f:
    for line in outfile:
      f.write(line+'\n')