System Vs Call Vs Popen In Python

cmd = 'touch -d '+date_in+' '+images_dir+'/'+photo_name os.system(cmd) Doesn't work subprocess.call(['touch','-d','{}'.format(date_in),'{}'.format(images_dir+'/'+photo_name)]) Do

Solution 1:

I wouldn't use touch at all for this; use os.utime instead.

import os

try:
    response = urllib2.urlopen(url)
except Exception as message:
    print'URL open exception {}'.format(message)
else:
    if response.getcode() == 200:
        photo_file = response.read()
        f = os.path.join(images_dir, photo_name)
        with open(f,'wb') as output:
            output.write(photo_file)
        os.utime(f, (date_in, date_in))

        f = os.path.join(images_dir, 'captions', photo_name + '.txt')    
        with open(f, 'wb') as output:
            output.write(photo_title)
    else:
        print'Download error'

Note that the date/time arguments to os.utime must be integer UNIX timestamps; you'll need to convert your date_in value from whatever it currently is first.

Solution 2:

Now it's clear:

with open(images_dir+'/'+photo_name,'wb') as output:
    output.write(photo_file)
    #cmd = 'touch -d '+date_in+' '+images_dir+'/'+photo_name
    #subprocess.Popen(['touch','-d','{}'.format(date_in),'{}'.format(images_dir+'/'+photo_name)])
    subprocess.check_call(['touch','-d','{}'.format(date_in),'{}'.format(images_dir+'/'+photo_name)])

My assumption is: you're still in the with block, so if check_call or system is performed, it ends, then the file is closed, setting the date again and ruining touch efforts.

With Popen, the process is performed in the background, so when it's executed, the file is already closed (well, actually it's a race condition, it's not guaranteed)

I suggest:

with open(images_dir+'/'+photo_name,'wb') as output:
    output.write(photo_file)
subprocess.check_call(['touch','-d','{}'.format(date_in),'{}'.format(images_dir+'/'+photo_name)])

so the file is properly closed when you call check_call

Better written:

fullpath = os.path.join(images_dir,photo_name)
withopen(fullpath ,'wb') as output:
    output.write(photo_file)
# we're outside the with block, note the de-indentation
subprocess.check_call(['touch','-d','{}'.format(date_in),fullpath])