1 import importlib.util
2 import sys
3 
4 
5 class VendorImporter:
6     """
7     A PEP 302 meta path importer for finding optionally-vendored
8     or otherwise naturally-installed packages from root_name.
9     """
10 
11     def __init__(self, root_name, vendored_names=(), vendor_pkg=None):
12         self.root_name = root_name
13         self.vendored_names = set(vendored_names)
14         self.vendor_pkg = vendor_pkg or root_name.replace('extern', '_vendor')
15 
16     @property
17     def search_path(self):
18         """
19         Search first the vendor package then as a natural package.
20         """
21         yield self.vendor_pkg + '.'
22         yield ''
23 
24     def _module_matches_namespace(self, fullname):
25         """Figure out if the target module is vendored."""
26         root, base, target = fullname.partition(self.root_name + '.')
27         return not root and any(map(target.startswith, self.vendored_names))
28 
29     def load_module(self, fullname):
30         """
31         Iterate over the search path to locate and load fullname.
32         """
33         root, base, target = fullname.partition(self.root_name + '.')
34         for prefix in self.search_path:
35             try:
36                 extant = prefix + target
37                 __import__(extant)
38                 mod = sys.modules[extant]
39                 sys.modules[fullname] = mod
40                 return mod
41             except ImportError:
42                 pass
43         else:
44             raise ImportError(
45                 "The '{target}' package is required; "
46                 "normally this is bundled with this package so if you get "
47                 "this warning, consult the packager of your "
48                 "distribution.".format(**locals())
49             )
50 
51     def create_module(self, spec):
52         return self.load_module(spec.name)
53 
54     def exec_module(self, module):
55         pass
56 
57     def find_spec(self, fullname, path=None, target=None):
58         """Return a module spec for vendored names."""
59         return (
60             importlib.util.spec_from_loader(fullname, self)
61             if self._module_matches_namespace(fullname) else None
62         )
63 
64     def install(self):
65         """
66         Install this importer into sys.meta_path if not already present.
67         """
68         if self not in sys.meta_path:
69             sys.meta_path.append(self)
70 
71 
72 names = (
73     'packaging', 'pyparsing', 'appdirs', 'jaraco', 'importlib_resources',
74     'more_itertools',
75 )
76 VendorImporter(__name__, names).install()
77