Syntax Error with Argument Parser

Syntax Error with Argument Parser - Printable Version

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Syntax Error with Argument Parser - aditya_man - Sep-30-2019

Hello all,
I was working on a project where I would separate the frames of an image using OpenCV using Argument Parser. It is something to do with the right way to pass argument parse variables as parameters for a function. This is what the error states.

File "video-frames.py", line 13
    def extractFrames('args.input', 'args.output'):
                                 ^
SyntaxError: invalid syntax

Below is my code:

import cv2
import os
import argparse

ap = argparse.ArgumentParser()

ap.add_argument("-i", "--input", required=True, help="path to input video")
ap.add_argument("-o", "--output", required=True, help="path to output directory")

args = vars(ap.parse_args())

#Function to extract frames
def extractFrames('args.input', 'args.output'):
   #directory path, where my video images will be stored
   #Capture vidoe from video file
   cap = cv2.VideoCapture(args["input"])
#Counter Variable
count = 0

while (cap.isOpened()):
   # Capture frame-by-frame
   ret, frame = cap.read()
   if ret == True:
      print('Read %d frame: ' % count, ret)
      # save frame as JPEG file
      cv2.imwrite(os.path.join(args["output"], "frame{:d}.png".format(count)), frame)
      count += 1
   else:
      break
# When everything done, release the capture
cap.release()
cv2.destroyAllWindows()
def main():
   extractFrames(args["input"] , args["output"])
if __name__=="__main__":
   main()

Any help in fixing this would be greatly appreciated.

Thank you so much,
Aditya

RE: Syntax Error with Argument Parser - ichabod801 - Sep-30-2019

Your parameter list for the extractFrames function is just two string literals. Parameters have to be valid Python tokens, not literal values. You can assign literal values to those tokens as default values for the parameters, so you could do something like this:

def extractFrames(input = 'args.input', output = 'args.output'):
   #directory path, where my video images will be stored
   #Capture vidoe from video file
   cap = cv2.VideoCapture(args["input"])

However, looking at the code, I think what you really want is this:

def extractFrames(args):
   #directory path, where my video images will be stored
   #Capture vidoe from video file
   return cv2.VideoCapture(args["input"])
cap = extractFrames(args)

You might want to check out the function tutorial for details on parameters and return values.