How do I run a Python script?

[markpatterson]

I would like to get past this hurdle: How do I do hello world in a Python script. I took the advice of http://developer.apple.com/unix/crossplatform.html, where they recommend doing this:

#!/usr/bin/env python

print "Hello!"

I saved that as hello.py, chmod +x'ed it, tried to run it and got this:

Pattersons-eMac:~/dev/scripts mark$ hello.py
print "Hello!": No such file or directory

What am I doing wrong? It seems to be ignoring python altogether.

TIA,

Mark

 

[scruffy]

python is in /usr/bin. Not sure where the /usr/bin/env comes from - or is that a typo? The first line should just be:
#!/usr/bin/python

As for the syntax - I don't know python, so I don't know if that's right or not...

 

[markpatterson]

python is in /usr/bin. Not sure where the /usr/bin/env comes from - or is that a typo? The first line should just be:
#!/usr/bin/python

As for the syntax - I don't know python, so I don't know if that's right or not...

I just copied that from the Apple page. See the link in my first post. That is their way to make it cross-platform, so that it will run on unices with things in different places.

I changed the script to:

#!/usr/bin/python

print "Hello!"

which is a link to the real python, and got this:

Pattersons-eMac:/usr/bin mark$ hello.py
print: bad interpreter: No such file or directory/python

The python is correct, though. I just tried this:

Pattersons-eMac:~/dev/scripts mark$ python hello.py
Hello!

 

[markpatterson]

I think I've solved it. I used HexEditor (www.ex-cinder.com), and found that the line breaks were 0D. I changed them to 0A and finally got

Pattersons-eMac:~ mark$ hello.py
Hello!

from

#! /usr/bin/env python

print "Hello!"

 

[scruffy]

interesting - from the env manpage:

env [-i] [name=value ...] [utility [argument ...]]

DESCRIPTION
env executes utility after modifying the environment as specified on the
command line. The option name=value specifies an environmental variable,
name, with a value of value. The option `-i' causes env to completely
ignore the environment it inherits.

So, in this case, "/usr/bin/env python" is exactly equivalent to "/usr/bin/python", since it doesn't alter any environment variables... I wonder why they do it that way then.

 

[markpatterson]

If you look at this page: http://python.org/doc/current/tut/node4.html there are 2 different places for python from /usr/bin:
"The Python interpreter is usually installed as /usr/local/bin/python ... /usr/local/python is a popular alternative location"

Down the page a few paragraphs it gives the same idea as the Apple page:
"On BSD'ish Unix systems, Python scripts can be made directly executable, like shell scripts, by putting the line

#! /usr/bin/env python

(assuming that the interpreter is on the user's PATH) at the beginning of the script"

So I guess env is used because it is always at that location, and can be used to find something on the path.