Import Module.

import_module.py

# ---
# published: true
# title: Importing Python Modules
# layout: post
# comments: true
# tags: python
# categories: post
# ---

# In the [previous post](/post/2018/09/06/peg-parsing/) I discussed how to
# implement simple parsing expression grammar based parsing, and I mentioned
# that the notebook is available in [runnable source form](https://github.com/rahulgopinath/rahulgopinath.github.io/blob/master/notebooks/2018-09-06-peg-parsing.py).
# This brings a question however. How do we make use of this notebook in later
# posts?

import sys, os, ast
import types
import importlib.abc
import importlib.machinery

class MetaPathFinderInWeb(importlib.abc.MetaPathFinder):
    def __init__(self, loaders): self._loaders = loaders

    def find_spec(self, fullname, path, target=None):
        for loader in self._loaders:
            if self._loaders[loader].has(fullname):
                return importlib.machinery.ModuleSpec(fullname, self._loaders[loader])
        return None

class LocalLoader(importlib.abc.SourceLoader):
    def __init__(self):
        self.locations = {}

    def get_data(self, m_loc):
            #m_loc = './notebooks/%s' % m_loc
            with open(m_loc, encoding='utf-8') as f: return f.read()

    def get_filename(self, fullname):
        return self.locations[fullname]

    def has(self, fullname): return fullname in self.locations

class WebLoader(importlib.abc.SourceLoader):
    def __init__(self):
        self.locations = {}

    def get_data(self, m_loc):
        import urllib.request
        github_repo = 'https://raw.githubusercontent.com/'
        my_repo =  'rahulgopinath/rahulgopinath.github.io'
        m_loc = github_repo + my_repo + '/master/notebooks/%s' % m_loc
        return urllib.request.urlopen(m_loc).read()

    def get_filename(self, fullname):
        return self.locations[fullname]

    def has(self, fullname): return fullname in self.locations

class PyodideLoader(importlib.abc.SourceLoader):
    def __init__(self):
        self.locations = {}

    def get_data(self, m_loc):
        if "pyodide" not in sys.modules: return None
        import pyodide
        github_repo = 'https://raw.githubusercontent.com/'
        my_repo =  'rahulgopinath/rahulgopinath.github.io'
        m_loc = github_repo + my_repo + '/master/notebooks/%s' % m_loc
        return pyodide.open_url(m_loc).getvalue()

    def get_filename(self, fullname):
        return self.locations[fullname]

    def has(self, fullname): return fullname in self.locations

class MyLoader(importlib.abc.Loader):
    def __init__(self):
        self.services = {}

    def has(self, fullname): return fullname in self.services

    def create_module(self, spec): return self.services[spec.name]

    def exec_module(self, module): pass

    def register(self, m_name, m_loc):
        mod_name, module = self.make_module(m_name, m_loc)
        if mod_name is None:
            m_loc
        self.services[mod_name] = module

    def get_module_src(self, m_loc):
        if "pyodide" in sys.modules:
            import pyodide
            github_repo = 'https://raw.githubusercontent.com/'
            my_repo =  'rahulgopinath/rahulgopinath.github.io'
            m_loc = github_repo + my_repo + '/master/notebooks/%s' % location
            module_str = pyodide.open_url(m_loc).getvalue()
        else:
            m_loc = './notebooks/%s' % m_loc
            with open(m_loc, encoding='utf-8') as f: return f.read()

    def make_module(self, m_name, m_loc):
        myast = ast.parse(self.get_module_src(m_loc), filename=m_loc, mode='exec')
        assert myast.body[-1].targets[0].id == '__MODULE_NAME__'               
        mod_name = myast.body[-1].value.s
        codeobj = compile(myast, m_loc, 'exec')
        assert codeobj.co_consts[-1] == mod_name
        newmodule = types.ModuleType(m_name)
        #newmodule = imp.new_module(m_name)
        exec(codeobj, newmodule.__dict__)
        return newmodule.__dict__.get('__MODULE_NAME__', None), newmodule

class Importer:

    def __init__(self):
        self._loader = {'my':MyLoader(), 'local':LocalLoader(), 'web': WebLoader(), 'pyodide': PyodideLoader()}
        sys.meta_path.append(MetaPathFinderInWeb(self._loader))

    def register(self, m_name, m_loc):
        self._loader['my'].register(m_name, m_loc)
        #if os.path.exists(m_loc):
        #    self._loader['local'].locations[m_name] = m_loc
        #elif "pyodide" in sys.modules:
        #    self._loader['pyodide'].locations[m_name] = m_loc
        #else:
        #    self._loader['web'].locations[m_name] = m_loc

importer = Importer()
importer.register("pegparser", '2018-09-06-peg-parsing.py')
import pegparser
print(pegparser.term_grammar)