:mod:py_compile --- Compile Python source files

.. module:: py_compile :synopsis: Generate byte-code files from Python source files.

.. sectionauthor:: Fred L. Drake, Jr. [email protected] .. documentation based on module docstrings

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.

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.

.. class:: PycInvalidationMode

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.