$ easy_install watchdog

#!/usr/bin/env python
import os, sys, time, subprocess

from watchdog.observers import Observer
from watchdog.events import FileSystemEventHandler

def log(s):
  print '[Monitor] %s' % s

class MyFileSystemEventHander(FileSystemEventHandler):
  def __init__(self, fn):
    super(MyFileSystemEventHander, self).__init__()
    self.restart = fn

  def on_any_event(self, event):
    if event.src_path.endswith('.py'):
      log('Python source file changed: %s' % event.src_path)
      self.restart()

command = ['echo', 'ok']
process = None

def kill_process():
  global process
  if process:
    log('Kill process [%s]...' % process.pid)
    process.kill()
    process.wait()
    log('Process ended with code %s.' % process.returncode)
    process = None

def start_process():
  global process, command
  log('Start process %s...' % ' '.join(command))
  process = subprocess.Popen(command, stdin=sys.stdin, stdout=sys.stdout, stderr=sys.stderr)

def restart_process():
  kill_process()
  start_process()

def start_watch(path, callback):
  observer = Observer()
  observer.schedule(MyFileSystemEventHander(restart_process), path, recursive=True)
  observer.start()
  log('Watching directory %s...' % path)
  start_process()
  try:
    while True:
      time.sleep(0.5)
  except KeyboardInterrupt:
    observer.stop()
  observer.join()

if __name__ == '__main__':
  argv = sys.argv[1:]
  if not argv:
    print('Usage: ./pymonitor your-script.py')
    exit(0)
  if argv[0]!='python':
    argv.insert(0, 'python')
  command = argv
  path = os.path.abspath('.')
  start_watch(path, None)

$ python pymonitor.py wsgiapp.py

$ ./pymonitor.py wsgiapp.py

$ ./pymonitor.py wsgiapp.py 
[Monitor] Watching directory /Users/michael/Github/awesome-python-webapp/www...
[Monitor] Start process python wsgiapp.py...
...
INFO:root:application (/Users/michael/Github/awesome-python-webapp/www) will start at 0.0.0.0:9000...
[Monitor] Python source file changed: /Users/michael/Github/awesome-python-webapp/www/apis.py
[Monitor] Kill process [2747]...
[Monitor] Process ended with code -9.
[Monitor] Start process python wsgiapp.py...
...
INFO:root:application (/Users/michael/Github/awesome-python-webapp/www) will start at 0.0.0.0:9000...
Try