Lib/py_compile.py

"""Routine to "compile" a .py file to a .pyc (or .pyo) file.

This module has intimate knowledge of the format of .pyc files.
"""

import __builtin__
import imp
import marshal
import os
import sys
import traceback

MAGIC = imp.get_magic()

__all__ = ["compile"]

# Define an internal helper according to the platform
if os.name == "mac":
    import macfs
    def set_creator_type(file):
        macfs.FSSpec(file).SetCreatorType('Pyth', 'PYC ')
else:
    def set_creator_type(file):
        pass

def wr_long(f, x):
    """Internal; write a 32-bit int to a file in little-endian order."""
    f.write(chr( x        & 0xff))
    f.write(chr((x >> 8)  & 0xff))
    f.write(chr((x >> 16) & 0xff))
    f.write(chr((x >> 24) & 0xff))

def compile(file, cfile=None, dfile=None):
    """Byte-compile one Python source file to Python bytecode.

    Arguments:

    file:  source filename
    cfile: target filename; defaults to source with 'c' or 'o' appended
           ('c' normally, 'o' in optimizing mode, giving .pyc or .pyo)
    dfile: purported filename; defaults to source (this is the filename
           that will show up in error messages)

    Note that it isn't necessary to byte-compile Python modules for
    execution efficiency -- Python itself byte-compiles a module when
    it is loaded, and if it can, writes out the bytecode to the
    corresponding .pyc (or .pyo) file.

    However, if a Python installation is shared between users, it is a
    good idea to byte-compile all modules upon installation, since
    other users may not be able to write in the source directories,
    and thus they won't be able to write the .pyc/.pyo file, and then
    they would be byte-compiling every module each time it is loaded.
    This can slow down program start-up considerably.

    See compileall.py for a script/module that uses this module to
    byte-compile all installed files (or all files in selected
    directories).

    """
    f = open(file, 'U')
    try:
        timestamp = long(os.fstat(f.fileno()).st_mtime)
    except AttributeError:
        timestamp = long(os.stat(file).st_mtime)
    codestring = f.read()
    f.close()
    if codestring and codestring[-1] != '\n':
        codestring = codestring + '\n'
    try:
        codeobject = __builtin__.compile(codestring, dfile or file, 'exec')
    except SyntaxError, detail:
        lines = traceback.format_exception_only(SyntaxError, detail)
        for line in lines:
            sys.stderr.write(line.replace('File "<string>"',
                                          'File "%s"' % (dfile or file)))
        return
    if cfile is None:
        cfile = file + (__debug__ and 'c' or 'o')
    fc = open(cfile, 'wb')
    fc.write('\0\0\0\0')
    wr_long(fc, timestamp)
    marshal.dump(codeobject, fc)
    fc.flush()
    fc.seek(0, 0)
    fc.write(MAGIC)
    fc.close()
    set_creator_type(cfile)