src/nmutil/noconflict.py

   1 import inspect
   2 import types
   3
   4 ############## preliminary: two utility functions #####################
   5
   6
   7 def skip_redundant(iterable, skipset=None):
   8     "Redundant items are repeated items or items in the original skipset."
   9     if skipset is None:
  10         skipset = set()
  11     for item in iterable:
  12         if item not in skipset:
  13             skipset.add(item)
  14             yield item
  15
  16
  17 def remove_redundant(metaclasses):
  18     skipset = set([type])
  19     for meta in metaclasses:  # determines the metaclasses to be skipped
  20         skipset.update(inspect.getmro(meta)[1:])
  21     return tuple(skip_redundant(metaclasses, skipset))
  22
  23 ##################################################################
  24 ## now the core of the module: two mutually recursive functions ##
  25 ##################################################################
  26
  27
  28 memoized_metaclasses_map = {}
  29
  30
  31 def get_noconflict_metaclass(bases, left_metas, right_metas):
  32     """Not intended to be used outside of this module, unless you know
  33     what you are doing."""
  34     # make tuple of needed metaclasses in specified priority order
  35     metas = left_metas + tuple(map(type, bases)) + right_metas
  36     needed_metas = remove_redundant(metas)
  37
  38     # return existing confict-solving meta, if any
  39     if needed_metas in memoized_metaclasses_map:
  40         return memoized_metaclasses_map[needed_metas]
  41     # nope: compute, memoize and return needed conflict-solving meta
  42     elif not needed_metas:         # wee, a trivial case, happy us
  43         meta = type
  44     elif len(needed_metas) == 1:  # another trivial case
  45         meta = needed_metas[0]
  46     # check for recursion, can happen i.e. for Zope ExtensionClasses
  47     elif needed_metas == bases:
  48         raise TypeError("Incompatible root metatypes", needed_metas)
  49     else:  # gotta work ...
  50         metaname = '_' + ''.join([m.__name__ for m in needed_metas])
  51         meta = classmaker()(metaname, needed_metas, {})
  52     memoized_metaclasses_map[needed_metas] = meta
  53     return meta
  54
  55
  56 def classmaker(left_metas=(), right_metas=()):
  57     def make_class(name, bases, adict):
  58         print("make_class", name)
  59         metaclass = get_noconflict_metaclass(bases, left_metas, right_metas)
  60         return metaclass(name, bases, adict)
  61     return make_class