"py_compile" — Compile Python source files
******************************************

**Source code:** Lib/py_compile.py

======================================================================

The "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 py_compile.PyCompileError

   Exception raised when an error occurs while attempting to compile
   the file.

py_compile.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
   "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, "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 "compile()" function.  The default of "-1" selects the
   optimization level of the current interpreter.

   *invalidation_mode* should be a member of the "PycInvalidationMode"
   enum and controls how the generated bytecode cache is invalidated
   at runtime.  The default is "PycInvalidationMode.CHECKED_HASH" if
   the "SOURCE_DATE_EPOCH" environment variable is set, otherwise the
   default is "PycInvalidationMode.TIMESTAMP".

   Changed in version 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.

   Changed in version 3.4: Changed code to use "importlib" for the
   byte-code cache file writing. This means file creation/writing
   semantics now match what "importlib" does, e.g. permissions, write-
   and-move semantics, etc. Also added the caveat that
   "FileExistsError" is raised if *cfile* is a symlink or non-regular
   file.

   Changed in version 3.7: The *invalidation_mode* parameter was added
   as specified in **PEP 552**. If the "SOURCE_DATE_EPOCH" environment
   variable is set, *invalidation_mode* will be forced to
   "PycInvalidationMode.CHECKED_HASH".

   Changed in version 3.7.2: The "SOURCE_DATE_EPOCH" environment
   variable no longer overrides the value of the *invalidation_mode*
   argument, and determines its default value instead.

class py_compile.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 Cached bytecode invalidation for more information on
   how Python invalidates ".pyc" files at runtime.

   New in version 3.7.

   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.

   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.

   UNCHECKED_HASH

      Like "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.

py_compile.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.

   Changed in version 3.2: Added support for "'-'".

When this module is run as a script, the "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.

See also:

  Module "compileall"
     Utilities to compile all Python source files in a directory tree.
