utils/scanpypi: allow installation of commands without 'main' method

In case the setup.py file of a python package does not directly call the
'setup' method, utils/scanpypi was hoping there be a 'main' function which
would do the work, normally called via a construct like:

    if __name__ == '__main__':
        main()

However, this construct is nonstandard, and there are packages in PyPI which
call 'setup()' directly from the 'if' statement, without a main() method.

But scanpypi does not actually need to make such assumption: when loading
the module, it can decide the name to be '__main__', just as if setup.py
would be loaded interactively.

Additionally, remove some logic seemingly related to the previous trick of
calling 'main'. There should not be a problem in keeping already loaded
modules in sys.modules, as this is the purpose of sys.modules.

Signed-off-by: Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

utils/scanpypi

@@ -299,7 +299,7 @@ class BuildrootPackage():
         os.chdir(self.tmp_extract)
         sys.path.insert(0,self.tmp_extract)
         s_file, s_path, s_desc = imp.find_module('setup', [self.tmp_extract])
-        setup = imp.load_module('setup', s_file, s_path, s_desc)
+        setup = imp.load_module('__main__', s_file, s_path, s_desc)
         if self.metadata_name in self.setup_args:
             pass
         elif self.metadata_name.replace('_', '-') in self.setup_args:
@@ -309,19 +309,10 @@ class BuildrootPackage():
         try:
             self.setup_metadata = self.setup_args[self.metadata_name]
         except KeyError:
-            # This means setup was not called which most likely mean that it is
-            # called through the if __name__ == '__main__' directive.
-            # In this case, we can only pray that it is called through a
-            # function called main() in setup.py.
-            setup.main()  # Will raise AttributeError if not found
-            self.setup_metadata = self.setup_args[self.metadata_name]
-        # Here we must remove the module the hard way.
-        # We must do this because of a very specific case: if a package calls
-        # setup from the __main__ but does not come with a 'main()' function,
-        # for some reason setup.main() will successfully call the main
-        # function of a previous package...
-        sys.modules.pop('setup', None)
-        del setup
+            # This means setup was not called
+            print('ERROR: Could not determine package metadata for {pkg}.\n'
+                  .format(pkg=self.real_name))
+            raise
         os.chdir(current_dir)
         sys.path.remove(self.tmp_extract)
 
@@ -706,7 +697,7 @@ def main():
                 else:
                     raise
                 continue
-            except AttributeError as error:
+            except (AttributeError, KeyError) as error:
                 print('Error: Could not install package {pkg}: {error}'.format(
                     pkg=package.real_name, error=error))
                 continue