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guriinii

Member

From: Rossendale

Registered: 2010-09-22

Posts: 84

Questions about python

I've just started learning python and I have some questions. Where do I save .py files and how do I make them executable?
I can run this in the directory it is stored in:

$ python helloworld.py
Hello World

but when I run 'python helloworld.py' or just 'helloworld.py' when in a different directory it doesn't work. Although I did:

$ chmod +x helloworld.py

to make it executable. Can anyone advise?

Also what is the difference between '#!/usr/bin/env python' and '#!/usr/bin/python'?

Last edited by guriinii (2010-10-12 23:01:36)

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The exponential learning curve.

karol

Archivist

Registered: 2009-05-06

Posts: 25,440

Re: Questions about python

To run executable files from any directory they have to be in your PATH:

echo $PATH

to see the current settings.
You can create e.g. ~/scripts and add that dir to the PATH. Now you put all your scripts there, make them executable and they should work.

Alternatively, you can create aliases / functions and put them in your ~/bashrc (or whatever you use):

alias whatdidido="sudo /home/karol/docs/code/whatdidido"

Last edited by karol (2010-10-12 23:27:18)

ewaller

Administrator

From: Pasadena, CA

Registered: 2009-07-13

Posts: 20,294

Re: Questions about python

Your working directory is probably not in $PATH

Try launching with  ./helloworld.py

You may also need to add the following as the first line in your file:

#!/usr/bin/python

Edit: Fixed #!,  The path is not /bin/python

Last edited by ewaller (2010-10-12 23:27:11)

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Nothing is too wonderful to be true, if it be consistent with the laws of nature -- Michael Faraday
Sometimes it is the people no one can imagine anything of who do the things no one can imagine. -- Alan Turing
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How to Ask Questions the Smart Way

karol

Archivist

Registered: 2009-05-06

Posts: 25,440

Re: Questions about python

@ ewaller
What about python2 / python3? If I want my script to use python2 how do I call it - #!/usr/bin/python2?

Edit: I am talking about http://mailman.archlinux.org/pipermail/ … 17653.html

Last edited by karol (2010-10-12 23:34:37)

ewaller

Administrator

From: Pasadena, CA

Registered: 2009-07-13

Posts: 20,294

Re: Questions about python

@ ewaller
What about python2 / python3? If I want my script to use python2 how do I call it? IIRC it was 'python2'.

/usr/bin/python is probably a symbolic link:

ewaller@odin:~ 1020 %which python
/usr/bin/python
ewaller@odin:~ 1021 %ls -l $(which python)
lrwxrwxrwx 1 root root 9 Mar 31  2010 /usr/bin/python -> python2.6
ewaller@odin:~ 1022 %

In my case, it runs python 2.6

If you want to explicitly run a particular version, change the 'crunch bang'  ( The #!) to point at the interpreter you desire:

#!/usr/bin/python2.6

or

#!/usr/bin/python3.0

etc...

Remember that the #! tells the system how to interpret the script.  That way the shell knows whether it is python, perl, bash, ruby, octave, whatever....

---

Nothing is too wonderful to be true, if it be consistent with the laws of nature -- Michael Faraday
Sometimes it is the people no one can imagine anything of who do the things no one can imagine. -- Alan Turing
---
How to Ask Questions the Smart Way

guriinii

Member

From: Rossendale

Registered: 2010-09-22

Posts: 84

Re: Questions about python

I'm reading A Byte Of Python - Swaroop CH and the answer was on the next page. ooops. I'm far too eager or impatient.

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The exponential learning curve.

kachelaqa

Member

Registered: 2010-09-26

Posts: 216

Re: Questions about python

Also what is the difference between '#!/usr/bin/env python' and '#!/usr/bin/python'?

distros may differ in where they install the python executables. python3 could be installed under /opt, for instance.

given this, it's more portable to use '#!/usr/bin/env python' (or '#!/usr/bin/env python3').

these forms will search for python in the $PATH rather than relying on a hard-coded location.

archman-cro

Member

From: Croatia

Registered: 2010-04-04

Posts: 943

Website

Re: Questions about python

Thanks for this info, kachelaqa. I was wondering what that means, too, but haven't researched on that topic.