invoke external program

edit

What is the proper way to call external applications in my programs? Specifically, pdfLaTeX compiler. When I invoke os.system("pdflatex foo.tex") in Sage's CLI console, the command executes as expected. However, when I embedded this into my code and run this code, TeX asks for another input:

This is pdfTeX, Version 3.1415926-1.40.10 (TeX Live 2009/Debian)
entering extended mode
(/tmp/foo.tex
LaTeX2e <2009/09/24>
Babel <v3.8l> and hyphenation patterns for english, usenglishmax, dumylang, noh
yphenation, loaded.
)
* [blinking cursor here]

Am I missing something or why doesn't this work?

P. S. My original post may have been confusing. When I wrote:

However, when I embedded this into my code and run this code,

I meant embedding into "my_code.sage" source code, which is consequently attached and run in Sage's CLI.

P. P. S. When use it in my "foo.sage" code as below:

os.system("pdflatex -interaction=batchmode foo.tex")

following log is produced:

(/tmp/foo.tex
LaTeX2e <2009/09/24>
Babel <v3.8l> and hyphenation patterns for english, usenglishmax, dumylang, noh
yphenation, loaded.
)
! Emergency stop.
<*> /tmp/foo.tex

*** (job aborted, no legal \end found)

However, written explicitly in Sage's console and even in bash console, everything compiles correctly. Does this mean something? Just FYI, I did end my source file with \end{document}