importlib.util.find_spec()

[Twirlip2]

Excuse me for following up my own post; also, for continuing to use Google
Groups (but I've been browsing news.gmane.org, with the intention of using
it in future - once I understand how to use it).

I should have read this:

<http://legacy.python.org/dev/peps/pep-0451/>
PEP 451 -- A ModuleSpec Type for the Import System
Status:	Final

 "*submodule_search_locations*
 
 The list of location strings, typically directory paths, in which to
 search for submodules. If the module is a package this will be set
 to a list (even an empty one). Otherwise it is None."

That explains the thing that was most puzzling me.

Here is the code I have written.  If you want to try it, you'll need to:
remove the 'self' argument; replace the methods self.prompt_print() and
self.prompt_input() with the functions print() and input() respectively;
replace the functions lines_in_file() and lines_of_code() with stubs, or
some useful functions of your own devising. (Of course, I'll post my own
code, if asked - but I don't want to make [more of?] a nuisance of myself
by posting a lot of irrelevant crap unasked!  My function lines_of_code()
doesn't work properly, anyway - for example, the script 'antigravity.py',
in the Python standard library, breaks it.)

(No doubt Google Groups will reformat this horribly:)

    def process(self):
        """Not documented yet; but see documentation for the abstract
        base class UserToken, whose process() function this overrides.
        See also 'PEP 451 -- A ModuleSpec Type for the Import System'.
        """

        while True:
            self.prompt_print('Type the name of a Python source code file')
            self.prompt_print('(omitting the invariable \'.py\' extension): ')
            name = self.prompt_input()
            if not name:
                return None # This is the only exit.
            else:
                spec = find_spec(name)
                if not spec:
                    print('\'%s\' is not on the Python search path.' % name)
                elif not spec.has_location:
                    print('\'%s\' is a Python built-in name.' % name)
                elif not hasattr(spec, 'submodule_search_locations'):
                    print('BUG (?): No submodule_search_locations for \'%s.\''
                        % name)
                else: # spec exists, and has the required attribute (a list).
                    submodules = spec.submodule_search_locations
                    if submodules is not None:
                        print('\'%s\' is a Python package (not built-in).'
                            % name)
                        if submodules:
                           print('Submodule search location(s):')
                           for s in submodules:
                              print(s)
                        else:
                            print('No submodule search locations are listed.')
                    elif not hasattr(spec, 'origin'):
                        print('BUG (?): No origin string for %s.py.' % name)
                    else: # attribute value is None, so this is not a package.
                        path = spec.origin
                        text = lines_in_file(path)
                        code = lines_of_code(path)
                        docs = text - code
                        print('\n%s\nis a Python source file consisting of'
                            % path)
                        print('%u lines of plain text, of which' % text)
                        print('%u are executable Python code, and' % code)
                        print('%u are docstrings, comments, or blank lines.\n'
                            % docs)