# 33.10. `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 `.pyc` files are invalidated at runtime. If the `SOURCE_DATE_EPOCH` environment variable is set, invalidation_mode will be forced to `PycInvalidationMode.CHECKED_HASH`.

  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`.

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.