Useful little python script for beginners

[pepperphd]

I've been studying Python for a few days, and wrote my first neat little script. It will compile your .py files into a .pyc, and chmod it for you so you can execute it from the shell with a ./filename



import py_compile #get the compile module
import sys #get the system module for argv
import os #get os so we can call chmod

if len(sys.argv) != 3:
#if the user didnt pass the correct amount of arguments
print "usage:", sys.argv[0],"infile","outfile"
#show them how to use it
quit()
#and exit

infile = sys.argv[1]
outfile = sys.argv[2]

py_compile.compile(infile, outfile)
#compile the .py to a .pyc (or whatever extension specified)

chmod_macro = "chmod +x " + outfile
#this command will allow the user to execute the outfile with a ./outfile

os.system(chmod_macro)
#execute the chmod macro

print "success!"
#and if all went well, inform the user and quit



This script will compile itself if you invoke it at the command line.


you@computer$ python pycompile.py pycompile.py pycompile.pycThat will generate a file called pycompile.pyc that you can invoke with a simple:

you@computer$ ./pycompile.pycThen use that script to further compile your python files.

you@computer$ ./pycompile.pyc otherpythonfile.py otherpythonfile.pyc I thought it was pretty neat and it demonstrates pythons simplicity and awesomeness.

[MrJoeyUK]

That's a handy script indeed, I think I'll take it! Thanks!

Will report back with how I got on with it. But how exactly does it work? Do I just add it onto a piece of code I've already written?

[pepperphd]

Edited to include in first post.

[MrJoeyUK]

Wow, it works great.. thanks for the further explaining.

No more typing python before my filenames!

[nvteighen]

Er... interesting, though the compiling part is just not necessary. You can execute scripts directly only by adding this as your first line in the script:



#!/usr/bin/env python


And then, chmod'ing it. The "Shebang" is not only used in Python, but in almost all scripting languages and it tells the shell to search for the correct interpreter. Chmod +x will give you execution permissions... executing it through calling the interpreter is actually regulated by the read permission :)

[pepperphd]

According to the Python documentation, "compiling" Python programs decreases the time it takes to load them into memory, so it has to be somewhat useful right?

[Can+~]

According to the Python documentation, "compiling" Python programs decreases the time it takes to load them into memory, so it has to be somewhat useful right?

When you run a python program:


python mything.py

It will get compiled immediately and be stored as a mything.pyc.

The second time you call it, it will go look at both timestamps: if the .py has been modified, it gets recompiled, otherwise, it just goes for the .pyc.

Also, you can force compilation using the -c flag.

[unutbu]

You can also use the incron package to monitor your ~/bin directory so that any file that is placed there is automatically chmod'ed to have execute permission.

[wmcbrine]

When you run a python program:


python mything.py

It will get compiled immediately and be stored as a mything.pyc.It won't -- the .pyc isn't saved for files launched that way. However, you can start an interactive session, and type "import mything"; that saves a .pyc. (Modules imported from a script are compiled and saved too, of course.)


Also, you can force compilation using the -c flag.That's not the function of "-c" that I'm seeing...

[wmcbrine]

chmod_macro = "chmod +x " + outfile
#this command will allow the user to execute the outfile with a ./outfile

os.system(chmod_macro)
#execute the chmod macro

Avoid the overhead of a system() call:


os.chmod(outfile, 0755)

[nvteighen]

What the interpreter does is to first compile the .py into a .pyc in memory and execute the compiled version. Python always will run compiled code.

But, of course, that is a loading overhead... That's why imported modules get compiled, to reduce time.

My comment was that compiling is not needed to make a Python script executable, but that the shebang and the execution permission are.

[Can+~]

It won't -- the .pyc isn't saved for files launched that way. However, you can start an interactive session, and type "import mything"; that saves a .pyc. (Modules imported from a script are compiled and saved too, of course.)

Forgot to say "in memory", but thank for correcting.


That's not the function of "-c" that I'm seeing...

I'm really surprised by this actually. I remember doing the -c before, now I'm reading the man pages and realize I didn't.

*edit: Now I get where I got confused, it was:

python -c "import py_compile; py_compile.compile('%f')"

which is pretty much what the code above does.