python noob: arg1 "must be string not tuple"?

agrestic · 01-07-2009, 05:35 AM

Code:

#!/usr/bin/python3
# Filename: vids.py

def watchVideo():
	import subprocess, os
	subprocess.call("ls $HOME/Videos", shell=True)
	movie = str(input('Copy & paste a video; hit Enter : '))
	var = "totem", movie
	os.system(var)

watchVideo()

I run it, input the filename, hit enter. And get the error:

Code:

Traceback (most recent call last):
  File "vids.py", line 11, in <module>
    watchVideo()
  File "vids.py", line 9, in watchVideo
    os.system(var)
TypeError: system() argument 1 must be string, not tuple

I'm new to both Bash and python (also ipython), & I'm using geany. I found this post a few hours earlier,https://www.linuxquestions.org/quest...uments-297277/ then learned about python's "import subprocess, os," etc. So this is my version of what randomx did. But if I try:

Code:

var = "totem" + movie

like randomx did, I get:
sh: totemtommy_emmanuel.mpg: not found
If I'm trying to do things with python a novice shouldn't consider, could anyone point me in the right direction? My current self-teaching list consists of the following:
1. http://wiki.python.org/moin/Beginner...NonProgrammers
2. http://www.redhatmagazine.com/2008/0...l-kept-secret/
3. http://docs.python.org/tutorial/
I haven't started #3 yet.

Edit: In Bash I would just do

Code:

PS3='>>> Type the # of a video & hit Enter: '

select video in $(ls *.mpg)
do
    exec totem $video
    break
done

exit 0

Thanks in advance.

bgeddy · 01-07-2009, 12:56 PM

Try putting a space in your program to add to the command line line like this :

Code:

	var = "totem " + movie

then run the code.

Haven't tested this but an initial look gives me this impression.

agrestic · 01-07-2009, 04:08 PM

Oh...my...god.

Well thank you kindly.
Pray tell, why did that 1 additional space after the program name make such a difference?

bgeddy · 01-07-2009, 04:29 PM

Quote:

Pray tell, why did that 1 additional space after the program name make such a difference?

Well the os.system(var) line is calling the operating system to execute the string that is the contents of var.

For expample - if var="ls -al" the the system call would have been like entering "ls -al" at the keyboard. Without the space the two strings would have no gap.

So in your example:

Code:

 
  var="totem" + "tommy_emmanuel.mpg"
# var now equals "totemtommy_emmanuel.mpg"
  os.system(var)
# tries to execute "totemtommy_emmanuel.mpg" - which will fail.

or :

Code:

 
  var="totem " + "tommy_emmanuel.mpg"
# var now equals "totem tommy_emmanuel.mpg"
  os.system(var)
# tries to execute "totem tommy_emmanuel.mpg" - which will succeed.

I didn't word that very well but I trust you get the idea..

jamescondron · 01-07-2009, 04:46 PM

Quick point, use 'raw_input' as opposed to 'input', try a more c string concat too, easier to maintain on larger strings, so is always good practice. Also, don't call modules in a method- once again its easier to maintain calling at top.

Try os.popen if you're using input and the os module; a lot more secure.

Give diveintopython.org a shot, a very, very good tutorial. With the above in mind, try

Code:

#!/usr/bin/env python

import os

def play_video():
    print os.popen("ls ~/video").read()
    var = raw_input("Please enter video\n>")
    try:
        os.popen("mplayer %s" % (var) )
    except:
        print "Some error occurred"
        raise SystemExit

if __name__ == '__main__':
    play_video()

agrestic · 01-07-2009, 06:03 PM

Quote:

Originally Posted by bgeddy

os.system(var)
# tries to execute "totemtommy_emmanuel.mpg" - which will fail.

...I trust you get the idea..

I spent about an hour looking up irrelevant python-related info &, shockingly

, came up with zilch. A plain English answer is refreshing, so thanks.

To jamesc, who said:
"Give diveintopython.org a shot, a very, very good tutorial."

Wilco, thanks; that site's new to me.

Ya know, I sucked at math in high school so programming's gonna be a real doozy. The most abstract thing I do is like, eh, distance divided into the difference in elevation is percent of slope, multiplied by the cosine of the zenith gives linear horizontal distance. As a surveyor, the only kind of math I understand is the kind where I can see the result, e.g., if I do a horizontal resection between deltas it creates a point to occupy & I physically stand there, so it's tangible.
But objects, whizbangs, tuples, jabberwockies, classes and doo-dads are hard as, well, learning a new language.

Wish me luck!
And thanks again.