This is a chunk of code I wrote for a job interview at some point - it is a remote key-value storage REST API supporting CRUD operations.

Maybe anyone has some feedback on this? It would be very helpful for me.

I did not attach the tests, since it might be a little bit too much code. You don't have to review both files - even commenting on just one can be extremely helpful.

remotekvs.py

# -*- test-case-name: tests.remotekvs_test.RemoteKVSTest -*-

import json
import inspect

from twisted.internet import reactor
from twisted.web.resource import Resource
from twisted.web.server import Site

from keyvaluestorage import KeyValueStorage


class RemoteKVSResource(Resource):
    """
    This is a Twisted Resource object used to serve requests for
    KeyValueStorage operations. It supports POST, GET, PUT and DELETE
    request methods and replies in JSON.
    """
    isLeaf = True

    def __init__(self):
        self.kvs = KeyValueStorage()

    def render(self, request):
        operations = {
            'POST': 'create',
            'GET': 'read',
            'PUT': 'update',
            'DELETE': 'delete'}
        if request.method in operations.keys():
            response = {
                'success': True}
            try:
                operation = getattr(self.kvs, operations[request.method])
                args = {k: v[0] if isinstance(v, list) else v
                        for k, v in request.args.items()}
                result = operation(**(args))
                if result is not None:
                    response['result'] = result
            except (TypeError, KeyValueStorage.KeyAlreadyExistsError,
                    KeyValueStorage.InvalidKeyError), exception:
                response['success'] = False
                response['error'] = exception.__class__.__name__
                if isinstance(exception, TypeError):
                    response['error_message'] = (
                        "Valid request parameters: %s." % (
                            ', '.join(inspect.getargspec(operation)[0][1:])))
                else:
                    response['error_message'] = str(exception)
        else:
            response = {
                'success': False,
                'error': 'InvalidRequestMethod',
                'error_message': (
                    "Valid request methods: POST, GET, PUT, DELETE.")}
        return json.dumps(response)


if __name__ == '__main__':  # pragma: no cover
    site = Site(RemoteKVSResource())
    reactor.listenTCP(2048, site)
    reactor.run()

keyvaluestorage.py

# -*- test-case-name: tests.keyvaluestorage_test.KeyValueStorageTest -*-


class KeyValueStorage(object):
    """The most basic key-value storage, supports all 4 CRUD operations."""

    class KeyAlreadyExistsError(Exception):
        """Key you are trying to create already exists in the database."""

    class InvalidKeyError(Exception):
        """Key you are trying to access does not exist in the database."""

    def __init__(self):
        self.storage = {}

    def create(self, key, value):
        if key in self.storage.keys():
            raise self.KeyAlreadyExistsError(
                ("Key already exists. KeyValueStorage does not allow "
                 "duplicate keys."))
        self.storage[key] = value

    def read(self, key):
        try:
            return self.storage[key]
        except KeyError:
            raise self.InvalidKeyError(
                "Key does not exist. You can not read by a nonexistent key.")

    def update(self, key, value):
        if key not in self.storage.keys():
            raise self.InvalidKeyError(
                "Key does not exist. You can not update by a nonexistent key.")
        self.storage[key] = value

    def delete(self, key):
        try:
            del self.storage[key]
        except KeyError:
            raise self.InvalidKeyError(
                "Key does not exist. You can not delete by a nonexistent key.")