py.py

class WaitForModification():
    "wait for /path/ file to be modified before exiting /with/ block"
    def __init__(self, path):
        self.path = path
        self.mtime = not os.path.exists(path) or os.path.getmtime(path)
    def __enter__(self):
        pass
    def __exit__(self, *args):
        while True:
            try:
                if os.path.getmtime(self.path)!=self.mtime: break
            except: pass
            time.sleep(0.01) #<------------------

...
with self.WaitForModification(fpath):
    ...