Convert all .py files to be valid Python

`raise NotImplementedError('Please replace this line with your code...')` signals to the user where they need to put their code.

This approach enables the codebase to be tested with lint tools like flake8, pyflakes, pylint, etc.

solutions/object_oriented_design/call_center/call_center.py

@@ -112,6 +112,11 @@ class CallCenter(object):
                 return employee
         return None
 
-    def notify_call_escalated(self, call):  # ...
+    def notify_call_escalated(self, call):
-    def notify_call_completed(self, call):  # ...
+        pass
-    def dispatch_queued_call_to_newly_freed_employee(self, call, employee):  # ...
+
+    def notify_call_completed(self, call):
+        pass
+
+    def dispatch_queued_call_to_newly_freed_employee(self, call, employee):
+        pass

solutions/object_oriented_design/deck_of_cards/deck_of_cards.py

@@ -92,7 +92,7 @@ class BlackJackHand(Hand):
 
     def possible_scores(self):
         """Return a list of possible scores, taking Aces into account."""
-        # ...
+        pass
 
 
 class Deck(object):
@@ -113,4 +113,5 @@ class Deck(object):
             return None
         return card
 
-    def shuffle(self):  # ...
+    def shuffle(self):
+        pass

solutions/object_oriented_design/lru_cache/lru_cache.py

@@ -11,9 +11,14 @@ class LinkedList(object):
         self.head = None
         self.tail = None
 
-    def move_to_front(self, node):  # ...
+    def move_to_front(self, node):
-    def append_to_front(self, node):  # ...
+        pass
-    def remove_from_tail(self):  # ...
+
+    def append_to_front(self, node):
+        pass
+
+    def remove_from_tail(self):
+        pass
 
 
 class Cache(object):

solutions/object_oriented_design/online_chat/online_chat.py

@@ -6,11 +6,20 @@ class UserService(object):
     def __init__(self):
         self.users_by_id = {}  # key: user id, value: User
 
-    def add_user(self, user_id, name, pass_hash):  # ...
+    def add_user(self, user_id, name, pass_hash):
-    def remove_user(self, user_id):  # ...
+        pass
-    def add_friend_request(self, from_user_id, to_user_id):  # ...
+
-    def approve_friend_request(self, from_user_id, to_user_id):  # ...
+    def remove_user(self, user_id):
-    def reject_friend_request(self, from_user_id, to_user_id):  # ...
+        pass
+
+    def add_friend_request(self, from_user_id, to_user_id):
+        pass
+
+    def approve_friend_request(self, from_user_id, to_user_id):
+        pass
+
+    def reject_friend_request(self, from_user_id, to_user_id):
+        pass
 
 
 class User(object):
@@ -25,12 +34,23 @@ class User(object):
         self.received_friend_requests_by_friend_id = {}  # key: friend id, value: AddRequest
         self.sent_friend_requests_by_friend_id = {}  # key: friend id, value: AddRequest
 
-    def message_user(self, friend_id, message):  # ...
+    def message_user(self, friend_id, message):
-    def message_group(self, group_id, message):  # ...
+        pass
-    def send_friend_request(self, friend_id):  # ...
+
-    def receive_friend_request(self, friend_id):  # ...
+    def message_group(self, group_id, message):
-    def approve_friend_request(self, friend_id):  # ...
+        pass
-    def reject_friend_request(self, friend_id):  # ...
+
+    def send_friend_request(self, friend_id):
+        pass
+
+    def receive_friend_request(self, friend_id):
+        pass
+
+    def approve_friend_request(self, friend_id):
+        pass
+
+    def reject_friend_request(self, friend_id):
+        pass
 
 
 class Chat(metaclass=ABCMeta):
@@ -51,8 +71,11 @@ class PrivateChat(Chat):
 
 class GroupChat(Chat):
 
-    def add_user(self, user):  # ...
+    def add_user(self, user):
-    def remove_user(self, user):  # ... 
+        pass
+
+    def remove_user(self, user):
+        pass
 
 
 class Message(object):

solutions/object_oriented_design/parking_lot/parking_lot.py

@@ -1,4 +1,5 @@
 from abc import ABCMeta, abstractmethod
+from enum import Enum
 
 
 class VehicleSize(Enum):
@@ -92,11 +93,11 @@ class Level(object):
 
     def _find_available_spot(self, vehicle):
         """Find an available spot where vehicle can fit, or return None"""
-        # ...
+        pass
 
     def _park_starting_at_spot(self, spot, vehicle):
         """Occupy starting at spot.spot_number to vehicle.spot_size."""
-        # ...
+        pass
 
 
 class ParkingSpot(object):
@@ -117,5 +118,8 @@ class ParkingSpot(object):
             return False
         return vehicle.can_fit_in_spot(self)
 
-    def park_vehicle(self, vehicle):  # ...
+    def park_vehicle(self, vehicle):
-    def remove_vehicle(self):  # ...
+        pass
+
+    def remove_vehicle(self):
+        pass

solutions/system_design/social_graph/social_graph_snippets.py

@@ -61,3 +61,4 @@ class UserGraphService(object):
     def bfs(self, source, dest):
         # Use self.visited_ids to track visited nodes
         # Use self.lookup to translate a person_id to a Person
+        pass

solutions/system_design/web_crawler/web_crawler_snippets.py

@@ -2,33 +2,33 @@
 
 class PagesDataStore(object):
 
-    def __init__(self, db);
+    def __init__(self, db):
         self.db = db
-        ...
+        pass
 
     def add_link_to_crawl(self, url):
         """Add the given link to `links_to_crawl`."""
-        ...
+        pass
 
     def remove_link_to_crawl(self, url):
         """Remove the given link from `links_to_crawl`."""
-        ...
+        pass
 
-    def reduce_priority_link_to_crawl(self, url)
+    def reduce_priority_link_to_crawl(self, url):
         """Reduce the priority of a link in `links_to_crawl` to avoid cycles."""
-        ...
+        pass
 
     def extract_max_priority_page(self):
         """Return the highest priority link in `links_to_crawl`."""
-        ...
+        pass
 
     def insert_crawled_link(self, url, signature):
         """Add the given link to `crawled_links`."""
-        ...
+        pass
 
     def crawled_similar(self, signature):
         """Determine if we've already crawled a page matching the given signature"""
-        ...
+        pass
 
 
 class Page(object):
@@ -41,7 +41,7 @@ class Page(object):
 
     def create_signature(self):
         # Create signature based on url and contents
-        ...
+        pass
 
 
 class Crawler(object):