Lib/xreload.py

"""Alternative to reload().

This works by executing the module in a scratch namespace, and then
patching classes, methods and functions.  This avoids the need to
patch instances.  New objects are copied into the target namespace.
"""

import imp
import sys
import types


def xreload(mod):
    """Reload a module in place, updating classes, methods and functions.

    Args:
      mod: a module object

    Returns:
      The (updated) input object itself.
    """
    # Get the module name, e.g. 'foo.bar.whatever'
    modname = mod.__name__
    # Get the module namespace (dict) early; this is part of the type check
    modns = mod.__dict__
    # Parse it into package name and module name, e.g. 'foo.bar' and 'whatever'
    i = modname.rfind(".")
    if i >= 0:
        pkgname, modname = modname[:i], modname[i+1:]
    else:
        pkgname = None
    # Compute the search path
    if pkgname:
        # We're not reloading the package, only the module in it
        pkg = sys.modules[pkgname]
        path = pkg.__path__  # Search inside the package
    else:
        # Search the top-level module path
        pkg  = None
        path = None  # Make find_module() uses the default search path
    # Find the module; may raise ImportError
    (stream, filename, (suffix, mode, kind)) = imp.find_module(modname, path)
    # Turn it into a code object
    try:
        # Is it Python source code or byte code read from a file?
        # XXX Could handle frozen modules, zip-import modules
        if kind not in (imp.PY_COMPILED, imp.PY_SOURCE):
            # Fall back to built-in reload()
            return reload(mod)
        if kind == imp.PY_SOURCE:
            source = stream.read()
            code = compile(source, filename, "exec")
        else:
            code = marshal.load(stream)
    finally:
        if stream:
            stream.close()
    # Execute the code im a temporary namespace; if this fails, no changes
    tmpns = {}
    exec(code, tmpns)
    # Now we get to the hard part
    oldnames = set(modns)
    newnames = set(tmpns)
    # Add newly introduced names
    for name in newnames - oldnames:
        modns[name] = tmpns[name]
    # Delete names that are no longer current
    for name in oldnames - newnames - {"__name__"}:
        del modns[name]
    # Now update the rest in place
    for name in oldnames & newnames:
        modns[name] = _update(modns[name], tmpns[name])
    # Done!
    return mod


def _update(oldobj, newobj):
    """Update oldobj, if possible in place, with newobj.

    If oldobj is immutable, this simply returns newobj.

    Args:
      oldobj: the object to be updated
      newobj: the object used as the source for the update

    Returns:
      either oldobj, updated in place, or newobj.
    """
    if type(oldobj) is not type(newobj):
        # Cop-out: if the type changed, give up
        return newobj
    if hasattr(newobj, "__reload_update__"):
        # Provide a hook for updating
        return newobj.__reload_update__(oldobj)
    if isinstance(newobj, types.ClassType):
        return _update_class(oldobj, newobj)
    if isinstance(newobj, types.FunctionType):
        return _update_function(oldobj, newobj)
    if isinstance(newobj, types.MethodType):
        return _update_method(oldobj, newobj)
    # XXX Support class methods, static methods, other decorators
    # Not something we recognize, just give up
    return newobj


def _update_function(oldfunc, newfunc):
    """Update a function object."""
    oldfunc.__doc__ = newfunc.__doc__
    oldfunc.__dict__.update(newfunc.__dict__)
    oldfunc.func_code = newfunc.func_code
    oldfunc.func_defaults = newfunc.func_defaults
    # XXX What else?
    return oldfunc


def _update_method(oldmeth, newmeth):
    """Update a method object."""
    # XXX What if im_func is not a function?
    _update_function(oldmeth.im_func, newmeth.im_func)
    return oldmeth


def _update_class(oldclass, newclass):
    """Update a class object."""
    # XXX What about __slots__?
    olddict = oldclass.__dict__
    newdict = newclass.__dict__
    oldnames = set(olddict)
    newnames = set(newdict)
    for name in newnames - oldnames:
        setattr(oldclass, name, newdict[name])
    for name in oldnames - newnames:
        delattr(oldclass, name)
    for name in oldnames & newnames - {"__dict__", "__doc__"}:
        setattr(oldclass, name,  newdict[name])
    return oldclass