text: """Import hook support.
  
  Consistent use of this module will make it possible to change the
  different mechanisms involved in loading modules independently.
  
  While the built-in module imp exports interfaces to the built-in
  module searching and loading algorithm, and it is possible to replace
  the built-in function __import__ in order to change the semantics of
  the import statement, until now it has been difficult to combine the
  effect of different __import__ hacks, like loading modules from URLs
  by rimport.py, or restricted execution by rexec.py.
  
  This module defines three new concepts:
  
  1) A "file system hooks" class provides an interface to a filesystem.
  
  One hooks class is defined (Hooks), which uses the interface provided
  by standard modules os and os.path.  It should be used as the base
  class for other hooks classes.
  
  2) A "module loader" class provides an interface to to search for a
  module in a search path and to load it.  It defines a method which
  searches for a module in a single directory; by overriding this method
  one can redefine the details of the search.  If the directory is None,
  built-in and frozen modules are searched instead.
  
  Two module loader class are defined, both implementing the search
  strategy used by the built-in __import__ function: ModuleLoader uses
  the imp module's find_module interface, while HookableModuleLoader
  uses a file system hooks class to interact with the file system.  Both
  use the imp module's load_* interfaces to actually load the module.
  
  3) A "module importer" class provides an interface to import a
  module, as well as interfaces to reload and unload a module.  It also
  provides interfaces to install and uninstall itself instead of the
  default __import__ and reload (and unload) functions.
  
  One module importer class is defined (ModuleImporter), which uses a
  module loader instance passed in (by default HookableModuleLoader is
  instantiated).
  
  The classes defined here should be used as base classes for extended
  functionality along those lines.
  
  If a module importer class supports dotted names, its import_module()
  must return a different value depending on whether it is called on
  behalf of a "from ... import ..." statement or not.  (This is caused
  by the way the __import__ hook is used by the Python interpreter.)  It
  would also do wise to install a different version of reload().
  
  """
  
  
  import __builtin__
  import imp
  import os
  import sys
  
  __all__ = ["BasicModuleLoader","Hooks","ModuleLoader","FancyModuleLoader",
             "BasicModuleImporter","ModuleImporter","install","uninstall"]
  
  VERBOSE = 0
  
  
  from imp import C_EXTENSION, PY_SOURCE, PY_COMPILED
  from imp import C_BUILTIN, PY_FROZEN, PKG_DIRECTORY
  BUILTIN_MODULE = C_BUILTIN
  FROZEN_MODULE = PY_FROZEN
  
  
  class _Verbose:
  
      def __init__(self, verbose = VERBOSE):
          self.verbose = verbose
  
      def get_verbose(self):
          return self.verbose
  
      def set_verbose(self, verbose):
          self.verbose = verbose
  
      # XXX The following is an experimental interface
  
      def note(self, *args):
          if self.verbose:
              self.message(*args)
  
      def message(self, format, *args):
          if args:
              print format%args
          else:
              print format
  
  
  class BasicModuleLoader(_Verbose):
  
      """Basic module loader.
  
      This provides the same functionality as built-in import.  It
      doesn't deal with checking sys.modules -- all it provides is
      find_module() and a load_module(), as well as find_module_in_dir()
      which searches just one directory, and can be overridden by a
      derived class to change the module search algorithm when the basic
      dependency on sys.path is unchanged.
  
      The interface is a little more convenient than imp's:
      find_module(name, [path]) returns None or 'stuff', and
      load_module(name, stuff) loads the module.
  
      """
  
      def find_module(self, name, path = None):
          if path is None:
              path = [None] + self.default_path()
          for dir in path:
              stuff = self.find_module_in_dir(name, dir)
              if stuff: return stuff
          return None
  
      def default_path(self):
          return sys.path
  
      def find_module_in_dir(self, name, dir):
          if dir is None:
              return self.find_builtin_module(name)
          else:
              try:
                  return imp.find_module(name, [dir])
              except ImportError:
                  return None
  
      def find_builtin_module(self, name):
          # XXX frozen packages?
          if imp.is_builtin(name):
              return None, '', ('', '', BUILTIN_MODULE)
          if imp.is_frozen(name):
              return None, '', ('', '', FROZEN_MODULE)
          return None
  
      def load_module(self, name, stuff):
          file, filename, info = stuff
          try:
              return imp.load_module(name, file, filename, info)
          finally:
              if file: file.close()
  
  
  class Hooks(_Verbose):
  
      """Hooks into the filesystem and interpreter.
  
      By deriving a subclass you can redefine your filesystem interface,
      e.g. to merge it with the URL space.
  
      This base class behaves just like the native filesystem.
  
      """
  
      # imp interface
      def get_suffixes(self): return imp.get_suffixes()
      def new_module(self, name): return imp.new_module(name)
      def is_builtin(self, name): return imp.is_builtin(name)
      def init_builtin(self, name): return imp.init_builtin(name)
      def is_frozen(self, name): return imp.is_frozen(name)
      def init_frozen(self, name): return imp.init_frozen(name)
      def get_frozen_object(self, name): return imp.get_frozen_object(name)
      def load_source(self, name, filename, file=None):
          return imp.load_source(name, filename, file)
      def load_compiled(self, name, filename, file=None):
          return imp.load_compiled(name, filename, file)
      def load_dynamic(self, name, filename, file=None):
          return imp.load_dynamic(name, filename, file)
      def load_package(self, name, filename, file=None):
          return imp.load_module(name, file, filename, ("", "", PKG_DIRECTORY))
  
      def add_module(self, name):
          d = self.modules_dict()
          if name in d: return d[name]
          d[name] = m = self.new_module(name)
          return m
  
      # sys interface
      def modules_dict(self): return sys.modules
      def default_path(self): return sys.path
  
      def path_split(self, x): return os.path.split(x)
      def path_join(self, x, y): return os.path.join(x, y)
      def path_isabs(self, x): return os.path.isabs(x)
      # etc.
  
      def path_exists(self, x): return os.path.exists(x)
      def path_isdir(self, x): return os.path.isdir(x)
      def path_isfile(self, x): return os.path.isfile(x)
      def path_islink(self, x): return os.path.islink(x)
      # etc.
  
      def openfile(self, *x): return open(*x)
      openfile_error = IOError
      def listdir(self, x): return os.listdir(x)
      listdir_error = os.error
      # etc.
  
  
  class ModuleLoader(BasicModuleLoader):
  
      """Default module loader; uses file system hooks.
  
      By defining suitable hooks, you might be able to load modules from
      other sources than the file system, e.g. from compressed or
      encrypted files, tar files or (if you're brave!) URLs.
  
      """
  
      def __init__(self, hooks = None, verbose = VERBOSE):
          BasicModuleLoader.__init__(self, verbose)
          self.hooks = hooks or Hooks(verbose)
  
      def default_path(self):
          return self.hooks.default_path()
  
      def modules_dict(self):
          return self.hooks.modules_dict()
  
      def get_hooks(self):
          return self.hooks
  
      def set_hooks(self, hooks):
          self.hooks = hooks
  
      def find_builtin_module(self, name):
          # XXX frozen packages?
          if self.hooks.is_builtin(name):
              return None, '', ('', '', BUILTIN_MODULE)
          if self.hooks.is_frozen(name):
              return None, '', ('', '', FROZEN_MODULE)
          return None
  
      def find_module_in_dir(self, name, dir, allow_packages=1):
          if dir is None:
              return self.find_builtin_module(name)
          if allow_packages:
              fullname = self.hooks.path_join(dir, name)
              if self.hooks.path_isdir(fullname):
                  stuff = self.find_module_in_dir("__init__", fullname, 0)
                  if stuff:
                      file = stuff[0]
                      if file: file.close()
                      return None, fullname, ('', '', PKG_DIRECTORY)
          for info in self.hooks.get_suffixes():
              suff, mode, type = info
              fullname = self.hooks.path_join(dir, name+suff)
              try:
                  fp = self.hooks.openfile(fullname, mode)
                  return fp, fullname, info
              except self.hooks.openfile_error:
                  pass
          return None
  
      def load_module(self, name, stuff):
          file, filename, info = stuff
          (suff, mode, type) = info
          try:
              if type == BUILTIN_MODULE:
                  return self.hooks.init_builtin(name)
              if type == FROZEN_MODULE:
                  return self.hooks.init_frozen(name)
              if type == C_EXTENSION:
                  m = self.hooks.load_dynamic(name, filename, file)
              elif type == PY_SOURCE:
                  m = self.hooks.load_source(name, filename, file)
              elif type == PY_COMPILED:
                  m = self.hooks.load_compiled(name, filename, file)
              elif type == PKG_DIRECTORY:
                  m = self.hooks.load_package(name, filename, file)
              else:
                  raise ImportError, "Unrecognized module type (%s) for %s" % \
                        (`type`, name)
          finally:
              if file: file.close()
          m.__file__ = filename
          return m
  
  
  class FancyModuleLoader(ModuleLoader):
  
      """Fancy module loader -- parses and execs the code itself."""
  
      def load_module(self, name, stuff):
          file, filename, (suff, mode, type) = stuff
          realfilename = filename
          path = None
  
          if type == PKG_DIRECTORY:
              initstuff = self.find_module_in_dir("__init__", filename, 0)
              if not initstuff:
                  raise ImportError, "No __init__ module in package %s" % name
              initfile, initfilename, initinfo = initstuff
              initsuff, initmode, inittype = initinfo
              if inittype not in (PY_COMPILED, PY_SOURCE):
                  if initfile: initfile.close()
                  raise ImportError, \
                      "Bad type (%s) for __init__ module in package %s" % (
                      `inittype`, name)
              path = [filename]
              file = initfile
              realfilename = initfilename
              type = inittype
  
          if type == FROZEN_MODULE:
              code = self.hooks.get_frozen_object(name)
          elif type == PY_COMPILED:
              import marshal
              file.seek(8)
              code = marshal.load(file)
          elif type == PY_SOURCE:
              data = file.read()
              code = compile(data, realfilename, 'exec')
          else:
              return ModuleLoader.load_module(self, name, stuff)
  
          m = self.hooks.add_module(name)
          if path:
              m.__path__ = path
          m.__file__ = filename
          exec code in m.__dict__
          return m
  
  
  class BasicModuleImporter(_Verbose):
  
      """Basic module importer; uses module loader.
  
      This provides basic import facilities but no package imports.
  
      """
  
      def __init__(self, loader = None, verbose = VERBOSE):
          _Verbose.__init__(self, verbose)
          self.loader = loader or ModuleLoader(None, verbose)
          self.modules = self.loader.modules_dict()
  
      def get_loader(self):
          return self.loader
  
      def set_loader(self, loader):
          self.loader = loader
  
      def get_hooks(self):
          return self.loader.get_hooks()
  
      def set_hooks(self, hooks):
          return self.loader.set_hooks(hooks)
  
      def import_module(self, name, globals={}, locals={}, fromlist=[]):
          name = str(name)
          if name in self.modules:
              return self.modules[name] # Fast path
          stuff = self.loader.find_module(name)
          if not stuff:
              raise ImportError, "No module named %s" % name
          return self.loader.load_module(name, stuff)
  
      def reload(self, module, path = None):
          name = str(module.__name__)
          stuff = self.loader.find_module(name, path)
          if not stuff:
              raise ImportError, "Module %s not found for reload" % name
          return self.loader.load_module(name, stuff)
  
      def unload(self, module):
          del self.modules[str(module.__name__)]
          # XXX Should this try to clear the module's namespace?
  
      def install(self):
          self.save_import_module = __builtin__.__import__
          self.save_reload = __builtin__.reload
          if not hasattr(__builtin__, 'unload'):
              __builtin__.unload = None
          self.save_unload = __builtin__.unload
          __builtin__.__import__ = self.import_module
          __builtin__.reload = self.reload
          __builtin__.unload = self.unload
  
      def uninstall(self):
          __builtin__.__import__ = self.save_import_module
          __builtin__.reload = self.save_reload
          __builtin__.unload = self.save_unload
          if not __builtin__.unload:
              del __builtin__.unload
  
  
  class ModuleImporter(BasicModuleImporter):
  
      """A module importer that supports packages."""
  
      def import_module(self, name, globals=None, locals=None, fromlist=None):
          parent = self.determine_parent(globals)
          q, tail = self.find_head_package(parent, str(name))
          m = self.load_tail(q, tail)
          if not fromlist:
              return q
          if hasattr(m, "__path__"):
              self.ensure_fromlist(m, fromlist)
          return m
  
      def determine_parent(self, globals):
          if not globals or not "__name__" in globals:
              return None
          pname = globals['__name__']
          if "__path__" in globals:
              parent = self.modules[pname]
              assert globals is parent.__dict__
              return parent
          if '.' in pname:
              i = pname.rfind('.')
              pname = pname[:i]
              parent = self.modules[pname]
              assert parent.__name__ == pname
              return parent
          return None
  
      def find_head_package(self, parent, name):
          if '.' in name:
              i = name.find('.')
              head = name[:i]
              tail = name[i+1:]
          else:
              head = name
              tail = ""
          if parent:
              qname = "%s.%s" % (parent.__name__, head)
          else:
              qname = head
          q = self.import_it(head, qname, parent)
          if q: return q, tail
          if parent:
              qname = head
              parent = None
              q = self.import_it(head, qname, parent)
              if q: return q, tail
          raise ImportError, "No module named " + qname
  
      def load_tail(self, q, tail):
          m = q
          while tail:
              i = tail.find('.')
              if i < 0: i = len(tail)
              head, tail = tail[:i], tail[i+1:]
              mname = "%s.%s" % (m.__name__, head)
              m = self.import_it(head, mname, m)
              if not m:
                  raise ImportError, "No module named " + mname
          return m
  
      def ensure_fromlist(self, m, fromlist, recursive=0):
          for sub in fromlist:
              if sub == "*":
                  if not recursive:
                      try:
                          all = m.__all__
                      except AttributeError:
                          pass
                      else:
                          self.ensure_fromlist(m, all, 1)
                  continue
              if sub != "*" and not hasattr(m, sub):
                  subname = "%s.%s" % (m.__name__, sub)
                  submod = self.import_it(sub, subname, m)
                  if not submod:
                      raise ImportError, "No module named " + subname
  
      def import_it(self, partname, fqname, parent, force_load=0):
          if not partname:
              raise ValueError, "Empty module name"
          if not force_load:
              try:
                  return self.modules[fqname]
              except KeyError:
                  pass
          try:
              path = parent and parent.__path__
          except AttributeError:
              return None
          partname = str(partname)
          stuff = self.loader.find_module(partname, path)
          if not stuff:
              return None
          fqname = str(fqname)
          m = self.loader.load_module(fqname, stuff)
          if parent:
              setattr(parent, partname, m)
          return m
  
      def reload(self, module):
          name = str(module.__name__)
          if '.' not in name:
              return self.import_it(name, name, None, force_load=1)
          i = name.rfind('.')
          pname = name[:i]
          parent = self.modules[pname]
          return self.import_it(name[i+1:], name, parent, force_load=1)
  
  
  default_importer = None
  current_importer = None
  
  def install(importer = None):
      global current_importer
      current_importer = importer or default_importer or ModuleImporter()
      current_importer.install()
  
  def uninstall():
      global current_importer
      current_importer.uninstall()
  