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Say a bit more about .pyc and .pyo files.

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Guido van Rossum 1998-05-29 19:12:23 +00:00
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Doc/tut/tut.tex
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@ -1876,7 +1876,7 @@ module search path. See the section on Standard Modules later.
As an important speed-up of the start-up time for short programs that
use a lot of standard modules, if a file called \file{spam.pyc} exists
in the directory where \file{spam.py} is found, this is assumed to
contain an already-``compiled'' version of the module \module{spam}.
contain an already-``byte-compiled'' version of the module \module{spam}.
The modification time of the version of \file{spam.py} used to create
\file{spam.pyc} is recorded in \file{spam.pyc}, and the file is
ignored if these don't match.
@ -1888,11 +1888,41 @@ this attempt fails; if for any reason the file is not written
completely, the resulting \file{spam.pyc} file will be recognized as
invalid and thus ignored later. The contents of the \file{spam.pyc}
file is platform independent, so a Python module directory can be
shared by machines of different architectures. (Tip for experts:
the module \module{compileall}\refstmodindex{compileall} creates
\file{.pyc} files for all modules.)
shared by machines of different architectures.
Some tips for experts:
\begin{itemize}
\item
When the Python interpreter is invoked with the \code{-O} flag,
optimized code is generated and stored in \file{.pyo} files.
The optimizer currently doesn't help much; it only removes
\keyword{assert} statements and \code{SET_LINENO} instructions.
When \code{-O} is used, \emph{all} bytecode is optimized; \code{.pyc}
files are ignored and \code{.py} files are compiled to optimized
bytecode.
\item
A program doesn't run any faster when it is read from a
\file{.pyc} or \file{.pyo} file than when it is read from a \file{.py}
file; the only thing that's faster about \file{.pyc} or \file{.pyo}
files is the speed with which they are loaded.
\item
It is possible to have a file called \file{spam.pyc} (or
\file{spam.pyo} when \code{-O} is used) without a module
\file{spam.py} in the same module. This can be used to distribute
a library of Python code in a form that is moderately hard to reverse
engineer.
\item
The module \module{compileall}\refstmodindex{compileall} can create
\file{.pyc} files (or \file{.pyo} files when \code{-O} is used) for
all modules in a directory.
\end{itemize}
% XXX Should optimization with -O be covered here?
\section{Standard Modules}
\label{standardModules}