Adding a timestamp to a file, python subprocess linux

Question

I’m trying to take a picture with my Raspicam on my raspberry and adding a timestamp too each picture. The code that I use doesn’t however work. It gives me a syntax error at .."+%H... I have mucked around in the code and was able too do it once, then tough the picture file didn’t receive any timestamp on it.

Does any one have any clue what im doing wrong?

#!/usr/bin/python

import RPi.GPIO as GPIO, time, os, subprocess, random

gpout = subprocess.check_output("stamp=$(date "+%H%M%S")", stderr=subprocess.STDOUT,shell=True)

gpout = subprocess.check_output("raspistill -t 1 --output /home/pi/photobooth_images/Test${stamp}.jpg", stderr=subprocess.STDOUT, shell=True)

Achilleas · Accepted Answer · 2014-04-16 15:46:13Z

1

Your syntax error is a basic lack of escaping the double quotes around the date format string. This is what is happening on the line which is causing the error:

gpout = subprocess.check_output("stamp=$(date "+%H%M%S")", stderr=subprocess.STDOUT,shell=True)
                                ^             ^       ^ ^
                    string begins    string ends      string begins and ends after )

You'll notice that the code colouring also signifies this. There are two ways to include a literal double-quote in a string:

Either escape the literal double quote

check_output("stamp=$(date \"+%H%M%S\")" ...

or use single quotes for string delimiters

check_output('stamp=$(date "+%H%M%S")' ...

answered Apr 16, 2014 at 15:46

Achilleas

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Comments

jfs · Accepted Answer · 2014-04-16 17:00:47Z

There are at least two issues:

to use double quotes inside a Python string literal, you should escape them or use single quotes for the string literal:
```
'stamp=$(date "+%H%M%S")'
```
it is pointless to set stamp shell variable because check_output() call spawns its own shell i.e., stamp won't be defined in the second command where you are trying to use it

You could emulate date "+%H%M%S" in Python:

import time
from subprocess import check_output, STDOUT

timestamp = time.strftime('%H%M%S')
path = '/home/pi/photobooth_images/Test{stamp}.jpg'.format(stamp=timestamp)
gpout = check_output(["raspistill", "-t", "1", "--output", path], stderr=STDOUT)

Note: shell=True is not used.

You could also format an existing datetime object:

from datetime import datetime

path = '/path/to/Test{now:%H%M%S}.jpg'.format(now=datetime.now())

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