palm_imputil.py

minimal python variant for small footprint apps like embedded apps

#
# imputil.py: import utilities
#
# Modified by J. Collins for the PalmOS
#

### docco needed here and in Docs/ ...

# note: avoid importing non-builtin modules
import imp                      ### not available in JPython?
import sys
import __builtin__

# for the DirectoryImporter
import marshal

__all__ = ["ImportManager","Importer","BuiltinImporter"]

_StringType = type('')
_ModuleType = type(sys)         ### doesn't work in JPython...

class ImportManager:
    "Manage the import process."

    def install(self, namespace=vars(__builtin__)):
        "Install this ImportManager into the specified namespace."

        if isinstance(namespace, _ModuleType):
            namespace = vars(namespace)

        # Note: we have no notion of "chaining"

        # Record the previous import hook, then install our own.
        self.previous_importer = namespace['__import__']
        self.namespace = namespace
        namespace['__import__'] = self._import_hook

        ### fix this
        # namespace['reload'] = self._reload_hook

    def uninstall(self):
        "Restore the previous import mechanism."
        self.namespace['__import__'] = self.previous_importer

    ######################################################################
    #
    # PRIVATE METHODS
    #

    def __init__(self, fs_imp=None):
        # Initialize the set of suffixes that we recognize and import.
        # The default will import dynamic-load modules first, followed by
        # .py files (or a .py file's cached bytecode)
        pass
    def _import_hook(self, fqname, globals=None, locals=None, fromlist=None):
        """Python calls this hook to locate and import a module."""

        parts = fqname.split('.')

        # determine the context of this import
        parent = self._determine_import_context(globals)

        # if there is a parent, then its importer should manage this import
        if parent:
            module = parent.__importer__._do_import(parent, parts, fromlist)
            if module:
                return module

        # has the top module already been imported?
        try:
            top_module = sys.modules[parts[0]]
        except KeyError:

            # look for the topmost module
            top_module = self._import_top_module(parts[0])
            if not top_module:
                # the topmost module wasn't found at all.
                raise ImportError, 'No module named ' + fqname

        # fast-path simple imports
        if len(parts) == 1:
            if not fromlist:
                return top_module

            if not top_module.__dict__.get('__ispkg__'):
                # __ispkg__ isn't defined (the module was not imported by us),
                # or it is zero.
                #
                # In the former case, there is no way that we could import
                # sub-modules that occur in the fromlist (but we can't raise an
                # error because it may just be names) because we don't know how
                # to deal with packages that were imported by other systems.
                #
                # In the latter case (__ispkg__ == 0), there can't be any sub-
                # modules present, so we can just return.
                #
                # In both cases, since len(parts) == 1, the top_module is also
                # the "bottom" which is the defined return when a fromlist
                # exists.
                return top_module

        importer = top_module.__dict__.get('__importer__')
        if importer:
            return importer._finish_import(top_module, parts[1:], fromlist)

        # If the importer does not exist, then we have to bail. A missing
        # importer means that something else imported the module, and we have
        # no knowledge of how to get sub-modules out of the thing.
        raise ImportError, 'No module named ' + fqname

    def _determine_import_context(self, globals):
        """Returns the context in which a module should be imported.

        The context could be a loaded (package) module and the imported module
        will be looked for within that package. The context could also be None,
        meaning there is no context -- the module should be looked for as a
        "top-level" module.
        """

        if not globals or not globals.get('__importer__'):
            # globals does not refer to one of our modules or packages. That
            # implies there is no relative import context (as far as we are
            # concerned), and it should just pick it off the standard path.
            return None

        # The globals refer to a module or package of ours. It will define
        # the context of the new import. Get the module/package fqname.
        parent_fqname = globals['__name__']

        # if a package is performing the import, then return itself (imports
        # refer to pkg contents)
        if globals['__ispkg__']:
            parent = sys.modules[parent_fqname]
            assert globals is parent.__dict__
            return parent

        i = parent_fqname.rfind('.')

        # a module outside of a package has no particular import context
        if i == -1:
            return None

        # if a module in a package is performing the import, then return the
        # package (imports refer to siblings)
        parent_fqname = parent_fqname[:i]
        parent = sys.modules[parent_fqname]
        assert parent.__name__ == parent_fqname
        return parent

    def _import_top_module(self, name):
        # scan sys.path looking for a location in the filesystem that contains
        # the module, or an Importer object that can import the module.
        for item in sys.path:
            module = item.import_top(name)
            if module:
                return module
        return None

    def _reload_hook(self, module):
        "Python calls this hook to reload a module."

        # reloading of a module may or may not be possible (depending on the
        # importer), but at least we can validate that it's ours to reload
        importer = module.__dict__.get('__importer__')
        if not importer:
            # Must have imported through some other mechanism - use builtin
            pass

        # okay. it is using the imputil system, and we must delegate it, but
        # we don't know what to do (yet)
        ### we should blast the module dict and do another get_code(). need to
        ### flesh this out and add proper docco...

        raise SystemError, "reload not yet implemented"


class Importer:
    "Base class for replacing standard import functions."

    def import_top(self, name):
        "Import a top-level module."
        return self._import_one(None, name, name)

    ######################################################################
    #
    # PRIVATE METHODS
    #
    def _finish_import(self, top, parts, fromlist):
        # if "a.b.c" was provided, then load the ".b.c" portion down from
        # below the top-level module.
        bottom = self._load_tail(top, parts)

        # if the form is "import a.b.c", then return "a"
        if not fromlist:
            # no fromlist: return the top of the import tree
            return top

        # the top module was imported by self.
        #
        # this means that the bottom module was also imported by self (just
        # now, or in the past and we fetched it from sys.modules).
        #
        # since we imported/handled the bottom module, this means that we can
        # also handle its fromlist (and reliably use __ispkg__).

        # if the bottom node is a package, then (potentially) import some
        # modules.
        #
        # note: if it is not a package, then "fromlist" refers to names in
        #       the bottom module rather than modules.
        # note: for a mix of names and modules in the fromlist, we will
        #       import all modules and insert those into the namespace of
        #       the package module. Python will pick up all fromlist names
        #       from the bottom (package) module; some will be modules that
        #       we imported and stored in the namespace, others are expected
        #       to be present already.
        if bottom.__ispkg__:
            self._import_fromlist(bottom, fromlist)

        # if the form is "from a.b import c, d" then return "b"
        return bottom

    def _import_one(self, parent, modname, fqname):
        "Import a single module."

        # has the module already been imported?
        try:
            return sys.modules[fqname]
        except KeyError:
            pass

        # load the module's code, or fetch the module itself
        result = self.get_code(parent, modname, fqname)
        if result is None:
            return None

        module = self._process_result(result, fqname)

        # insert the module into its parent
        if parent:
            setattr(parent, modname, module)
        return module

    def _process_result(self, (ispkg, code, values), fqname):
        # did get_code() return an actual module? (rather than a code object)
        is_module = isinstance(code, _ModuleType)