[open-craft-guild#3] Implement ISell wrapper to provide REPL

https://github.com/open-craft-guild/blueberrypy

Implement wrapper over default ipython repl to load blueberrypy app
modules and session

src/blueberrypy/ishell.py

@@ -0,0 +1,66 @@
+import importlib
+from IPython.terminal.interactiveshell import TerminalInteractiveShell
+from sqlalchemy.orm.session import sessionmaker
+
+
+class IShell(TerminalInteractiveShell):
+
+    def __init__(self, blueberrypy_config=None):
+        self._bbp_config = blueberrypy_config
+
+        try:
+            app_mod = importlib.import_module(self.get_package_name())
+        except:
+            app_mod = None
+
+        super(IShell, self).__init__(
+            user_ns=self.get_user_namespace(),
+            user_module=app_mod,
+            display_completions='multicolumn',  # oldstyle is 'readlinelike'
+            mouse_support=True,
+            space_for_menu=10,  # reserve N lines for the completion menu
+        )
+
+    def make_sqlalchemy_engine(self, prefix="sqlalchemy_engine"):
+
+        config = self._bbp_config.sqlalchemy_config
+
+        if prefix in config:
+            section = config[prefix]
+            from sqlalchemy.engine import engine_from_config
+            return engine_from_config(section, '')
+        else:
+            engine_bindings = {}
+            for section_name, section in config.viewitems():
+                if section_name.startswith(prefix):
+                    model_fqn = section_name[len(prefix) + 1:]
+                    model_fqn_parts = model_fqn.rsplit('.', 1)
+                    model_mod = __import__(model_fqn_parts[0], globals(), locals(), [model_fqn_parts[1]])
+                    model = getattr(model_mod, model_fqn_parts[1])
+                    engine_bindings[model] = engine_from_config(section)
+            return engine_bindings
+
+
+    def get_package_name(self):
+        config = self._bbp_config
+        return config.project_metadata and config.project_metadata["package"]
+
+    def get_user_namespace(self):
+        ns = {'__name__': 'blueberrypy-ishell'}
+        config = self._bbp_config
+        if config.use_sqlalchemy:
+            engine = self.make_sqlalchemy_engine()
+            if isinstance(engine, dict):
+                Session = sessionmaker(twophase=True)
+                Session.configure(binds=engine)
+            else:
+                Session = sessionmaker()
+                Session.configure(bind=engine)
+            model = importlib.import_module(self.get_package_name() + ".model")
+
+            metadata = model.metadata
+            metadata.bind = engine
+
+            ns['session'] = session = Session()
+            session.bind.echo = True
+        return ns