Crude memoization helper

example.py

@@ -4,23 +4,42 @@ import json
 STATE_FILE = 'wideq_state.json'
 
 
-def load_state():
+class Memo(object):
-    """Load the current state data for this example.
+    """Store memoization data persistently in a JSON file.
     """
 
-    try:
+    def __init__(self, filename):
-        with open(STATE_FILE) as f:
+        self.filename = filename
-            return json.load(f)
+        self.load()
-    except IOError:
-        return {}
 
+    def load(self):
+        """Load the current memoization data."""
+        try:
+            with open(self.filename) as f:
+                self.state = json.load(f)
+        except IOError:
+            self.state = {}
 
-def save_state(state):
+    def save(self):
-    """Dump the current state to disk.
+        """Dump the current state to disk."""
-    """
+        with open(self.filename, 'w') as f:
+            json.dump(self.state, f)
 
-    with open(STATE_FILE, 'w') as f:
+    def call(self, fn, key=None):
-        json.dump(state, f)
+        """Call a function using memoization.
+
+        You can either specify a memoization key explicitly or, by
+        default, use the function's `__name__`.
+        """
+
+        key = key or fn.__name__
+        if key in self.state:
+            return self.state[key]
+        else:
+            ret = fn()
+            self.state[key] = ret
+            self.save()
+            return ret
 
 
 def print_devices(devices):
@@ -28,36 +47,43 @@ def print_devices(devices):
         print(device['alias'])
 
 
+def endpoints():
+    gw = wideq.gateway_info()
+    return {
+        'oauth_base': gw['empUri'],
+        'api_root': gw['thinqUri'],
+    }
+
+
+def login(oauth_base):
+    login_url = wideq.oauth_url(oauth_base)
+    print('Log in here:')
+    print(login_url)
+    print('Then paste the URL where the browser is redirected:')
+    callback_url = input()
+    return wideq.parse_oauth_callback(callback_url)
+
+
+def start_session(api_root, access_token):
+    session_info = wideq.login(api_root, access_token)
+    print_devices(session_info['item'])
+    return session_info['jsessionId']
+
+
 def example():
-    state = load_state()
+    memo = Memo(STATE_FILE)
 
     # Get the URLs for the API.
-    if 'oauth_base' not in state and 'api_root' not in state:
+    ep = memo.call(endpoints)
-        gw = wideq.gateway_info()
+    oauth_base = ep['oauth_base']
-        state['oauth_base'] = gw['empUri']
+    api_root = ep['api_root']
-        state['api_root'] = gw['thinqUri']
-        save_state(state)
-    oauth_base = state['oauth_base']
-    api_root = state['api_root']
 
-    # If we don't have an access token, authenticate.
+    # Authenticate to get an access token.
-    if 'access_token' not in state:
+    access_token = memo.call(lambda: login(oauth_base), 'access_token')
-        login_url = wideq.oauth_url(oauth_base)
-        print('Log in here:')
-        print(login_url)
-        print('Then paste the URL where the browser is redirected:')
-        callback_url = input()
-        state['access_token'] = wideq.parse_oauth_callback(callback_url)
-        save_state(state)
-    access_token = state['access_token']
 
     # If we don't have a session, log in.
-    if 'session_id' not in state:
+    session_id = memo.call(lambda: start_session(api_root, access_token),
-        session_info = wideq.login(api_root, access_token)
+                           'session_id')
-        state['session_id'] = session_info['jsessionId']
-        save_state(state)
-        print_devices(session_info['item'])
-    session_id = state['session_id']
 
     # Request a list of devices.
     devices = wideq.get_devices(api_root, access_token, session_id)