Getting latest modified file and passing as input to a subprocess

Question

I have code which prints the latest file path of an image snapshot that is saved when motion is activated, I'm trying to use this file path as input to the next part of my code which converts the image to leave only the blue blobs. Any help is appreciated, I'm new to code.

#!/bin/bash/python

import os
from subprocess import  check_call

path = '/..'
os.chdir(path)
files = sorted(os.listdir(os.getcwd()), key=os.path.getmtime)

newest = files[-1]
if newest == "Thumbs.db":
        'newest = files[-1]

newest = [path+"/"+newest]
a = newest

print newest

##### convert to blue blobs

check_call(["sudo","convert","imgIn.jpg", "-posterize","2","imgOut.jpg"])

check_call([ "sudo",'convert', 'imgIn.jpg', '-matte', '(', '+clone', '-fuzz',     57%', '-opaque', 'black', '-transparent', 'blue', ')', '-compose', 'DstOut', '-    composite', 'imgOut.jpg'])

How do I use the file path of newest as imgIn.jpg?

Answer 1

Writing a function called get_latest_file():

from os.path import isabs, getmtime
from os import getcwd, listdir, path


def get_latest_file(p):
    if not isabs(p):
        p = path.join(getcwd(), p)
    files = sorted([path.join(p, x) for x in listdir(p)], key=getmtime)
    return (files and files[-1]) or None

This will get you the latest file sorted by modified time and returning the last/newest matching file for a given directory.

Note: One thing to note here in the above function is that you need to build up a list of absolute paths for the sorting key getmtime() to work correctly or it will throw OSError(s) since os.listdir() gives you a list of "names" in a given directory as relative names.

Example:

get_latest_file("images")

Then you can pass the result of this to your check_output() call:

latest_image = get_latest_file("images")
check_call(["sudo", "convert", latest_image, "-posterize", "2", "imgOut.jpg"])

Update: You could then finish this off by writing one more function called convert_image() like this:

from os.path impomrt splitext
from subprocess import check_call


def convert_image(inf):
    base, ext = splitext(inf)
    outf = "{0:s}-converted{1:s}".format(base, ext)
    check_call(["sudo", "convert", inf, "-posterize", "2", outf])

Update #2: In terms of passing in the path for get_latest_file() you have probably three choices here:

IMAGE_PATH = "/path/to/images"                   # hard coded

image_path = raw_input("Enter path to image: ")  # prompt user

image_path = sys.argv[1]                         # from the command line

Side Note: Your Shebang is not quite right; it should read: #!/usr/bin/env python

References:

• os
• sys
• os.path
• raw_input
• subprocess