.. module:: py_compile :synopsis: Generate byte-code files from Python source files.
.. sectionauthor:: Fred L. Drake, Jr. <fdrake@acm.org>
Source code: :source:`Lib/py_compile.py`
.. index:: pair: file; byte-code
The :mod:`py_compile` module provides a function to generate a byte-code file from a source file, and another function used when the module source file is invoked as a script.
Though not often needed, this function can be useful when installing modules for shared use, especially if some of the users may not have permission to write the byte-code cache files in the directory containing the source code.
.. exception:: PyCompileError Exception raised when an error occurs while attempting to compile the file.
.. function:: compile(file, cfile=None, dfile=None, doraise=False, optimize=-1, invalidation_mode=PycInvalidationMode.TIMESTAMP) Compile a source file to byte-code and write out the byte-code cache file. The source code is loaded from the file named *file*. The byte-code is written to *cfile*, which defaults to the :pep:`3147`/:pep:`488` path, ending in ``.pyc``. For example, if *file* is ``/foo/bar/baz.py`` *cfile* will default to ``/foo/bar/__pycache__/baz.cpython-32.pyc`` for Python 3.2. If *dfile* is specified, it is used as the name of the source file in error messages when instead of *file*. If *doraise* is true, a :exc:`PyCompileError` is raised when an error is encountered while compiling *file*. If *doraise* is false (the default), an error string is written to ``sys.stderr``, but no exception is raised. This function returns the path to byte-compiled file, i.e. whatever *cfile* value was used. The *doraise* and *quiet* arguments determine how errors are handled while compiling file. If *quiet* is 0 or 1, and *doraise* is false, the default behaviour is enabled: an error string is written to ``sys.stderr``, and the function returns ``None`` instead of a path. If *doraise* is true, a :exc:`PyCompileError` is raised instead. However if *quiet* is 2, no message is written, and *doraise* has no effect. If the path that *cfile* becomes (either explicitly specified or computed) is a symlink or non-regular file, :exc:`FileExistsError` will be raised. This is to act as a warning that import will turn those paths into regular files if it is allowed to write byte-compiled files to those paths. This is a side-effect of import using file renaming to place the final byte-compiled file into place to prevent concurrent file writing issues. *optimize* controls the optimization level and is passed to the built-in :func:`compile` function. The default of ``-1`` selects the optimization level of the current interpreter. *invalidation_mode* should be a member of the :class:`PycInvalidationMode` enum and controls how the generated bytecode cache is invalidated at runtime. The default is :attr:`PycInvalidationMode.CHECKED_HASH` if the :envvar:`SOURCE_DATE_EPOCH` environment variable is set, otherwise the default is :attr:`PycInvalidationMode.TIMESTAMP`. .. versionchanged:: 3.2 Changed default value of *cfile* to be :PEP:`3147`-compliant. Previous default was *file* + ``'c'`` (``'o'`` if optimization was enabled). Also added the *optimize* parameter. .. versionchanged:: 3.4 Changed code to use :mod:`importlib` for the byte-code cache file writing. This means file creation/writing semantics now match what :mod:`importlib` does, e.g. permissions, write-and-move semantics, etc. Also added the caveat that :exc:`FileExistsError` is raised if *cfile* is a symlink or non-regular file. .. versionchanged:: 3.7 The *invalidation_mode* parameter was added as specified in :pep:`552`. If the :envvar:`SOURCE_DATE_EPOCH` environment variable is set, *invalidation_mode* will be forced to :attr:`PycInvalidationMode.CHECKED_HASH`. .. versionchanged:: 3.7.2 The :envvar:`SOURCE_DATE_EPOCH` environment variable no longer overrides the value of the *invalidation_mode* argument, and determines its default value instead. .. versionchanged:: 3.8 The *quiet* parameter was added.
A enumeration of possible methods the interpreter can use to determine
whether a bytecode file is up to date with a source file. The .pyc file
indicates the desired invalidation mode in its header. See
:ref:`pyc-invalidation` for more information on how Python invalidates
.pyc files at runtime.
.. versionadded:: 3.7
.. attribute:: TIMESTAMP The ``.pyc`` file includes the timestamp and size of the source file, which Python will compare against the metadata of the source file at runtime to determine if the ``.pyc`` file needs to be regenerated.
.. attribute:: CHECKED_HASH The ``.pyc`` file includes a hash of the source file content, which Python will compare against the source at runtime to determine if the ``.pyc`` file needs to be regenerated.
.. attribute:: UNCHECKED_HASH Like :attr:`CHECKED_HASH`, the ``.pyc`` file includes a hash of the source file content. However, Python will at runtime assume the ``.pyc`` file is up to date and not validate the ``.pyc`` against the source file at all. This option is useful when the ``.pycs`` are kept up to date by some system external to Python like a build system.
.. function:: main(args=None) Compile several source files. The files named in *args* (or on the command line, if *args* is ``None``) are compiled and the resulting byte-code is cached in the normal manner. This function does not search a directory structure to locate source files; it only compiles files named explicitly. If ``'-'`` is the only parameter in args, the list of files is taken from standard input. .. versionchanged:: 3.2 Added support for ``'-'``.
When this module is run as a script, the :func:`main` is used to compile all the files named on the command line. The exit status is nonzero if one of the files could not be compiled.
.. seealso:: Module :mod:`compileall` Utilities to compile all Python source files in a directory tree.
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