title: Syntax for ap.add_argument()
body: <p>I am new to OpenCV. I am using anaconda spyder console to write Python code. I took code form here (<a href="https://www.pyimagesearch.com/2014/08/25/4-point-opencv-getperspective-transform-example/" rel="nofollow noreferrer">https://www.pyimagesearch.com/2014/08/25/4-point-opencv-getperspective-transform-example/</a>)
  The code was that I am struck at is:</p>
  
  <pre><code># USAGE
  # python transform_example.py --image images/example_01.png --coords "[(73, 239), (356, 117), (475, 265), (187, 443)]"
  # python transform_example.py --image images/example_02.png --coords "[(101, 185), (393, 151), (479, 323), (187, 441)]"
  # python transform_example.py --image images/example_03.png --coords "[(63, 242), (291, 110), (361, 252), (78, 386)]"
  
  # import the necessary packages
  from pyimagesearch.transform import four_point_transform
  import numpy as np
  import argparse
  import cv2
  
  # construct the argument parse and parse the arguments
  ap = argparse.ArgumentParser()
  ap.add_argument("-i", "--image", help = "path to the image file")
  ap.add_argument("-c", "--coords",
      help = "comma seperated list of source points")
  args = vars(ap.parse_args())
  
  # load the image and grab the source coordinates (i.e. the list of
  # of (x, y) points)
  # NOTE: using the 'eval' function is bad form, but for this example
  # let's just roll with it -- in future posts I'll show you how to
  # automatically determine the coordinates without pre-supplying them
  image = cv2.imread(args["image"])
  pts = np.array(eval(args["coords"]), dtype = "float32")
  
  # apply the four point tranform to obtain a "birds eye view" of
  # the image
  warped = four_point_transform(image, pts)
  
  # show the original and warped images
  cv2.imshow("Original", image)
  cv2.imshow("Warped", warped)
  cv2.waitKey(0)
  </code></pre>
  
  <p>At line no. 13 - 17 can someone tell exactly what is happening. I know that I need to get image, get coordinates of paper (and these lines are for this purpose) but I can't get image file.</p>