title: ValueError :must start with a character '-'
body: <pre><code>import numpy as np
  import argparse
  import cv2
  ap=argparse.ArgumentParser()
  ap.add_argument("-i","D:\python learning\IMG_20130614_000526.jpg",required=True,help="path to input image")
  ap.add_argument("-p","D:\python learning\deep-learning-face-detection\deploy.prototxt.txt",required=True,help="path to Caffe 'deploy' prototxt file")
  ap.add_argument("-m","D:\python learning\deep-learning-face-detection\res10_300x300_ssd_iter_140000.caffemodel",required=True,help="path to Caffe pretrained model")
  ap.add_argument("-c", "--confidence",type=float,default=0.5,help="minimum probability to filter weak detections")
  args=vars(ap.parse_args())
  </code></pre>
  
  <p>Error:</p>
  
  <pre><code>Traceback (most recent call last):
    File "D:\python learning\detectfaces.py", line 6, in &lt;module&gt;
      ap.add_argument("-p","D:\python learning\deep-learning-face-detection\deploy.prototxt.txt",required=True,help="path to Caffe 'deploy' prototxt file")
    File "C:\Users\RAJKUMAR\AppData\Local\Programs\Python\Python36-32\lib\argparse.py", line 1320, in add_argument
      kwargs = self._get_optional_kwargs(*args, **kwargs)
    File "C:\Users\RAJKUMAR\AppData\Local\Programs\Python\Python36-32\lib\argparse.py", line 1451, in _get_optional_kwargs
      raise ValueError(msg % args)
  ValueError: invalid option string 'D:\\python learning\\deep-learning-face-detection\\deploy.prototxt.txt': must start with a character '-'
  &gt;&gt;&gt;
  </code></pre>