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 @@ def _dispatch_call(self, call, employees):
                 return employee
         return None
 
-    def notify_call_escalated(self, call):  # ...
-    def notify_call_completed(self, call):  # ...
-    def dispatch_queued_call_to_newly_freed_employee(self, call, employee):  # ...
+    def notify_call_escalated(self, call):
+        pass
+
+    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 @@ def score(self):
 
     def possible_scores(self):
         """Return a list of possible scores, taking Aces into account."""
-        # ...
+        pass
 
 
 class Deck(object):
@@ -113,4 +113,5 @@ def deal_card():
             return None
         return card
 
-    def shuffle(self):  # ...
+    def shuffle(self):
+        pass

solutions/object_oriented_design/lru_cache/lru_cache.py

@@ -11,9 +11,14 @@ def __init__(self):
         self.head = None
         self.tail = None
 
-    def move_to_front(self, node):  # ...
-    def append_to_front(self, node):  # ...
-    def remove_from_tail(self):  # ...
+    def move_to_front(self, node):
+        pass
+
+    def append_to_front(self, node):
+        pass
+
+    def remove_from_tail(self):
+        pass
 
 
 class Cache(object):
@@ -26,7 +31,7 @@ def __init__(self, MAX_SIZE):
 
     def get(self, query)
         """Get the stored query result from the cache.
-        
+
         Accessing a node updates its position to the front of the LRU list.
         """
         node = self.lookup[query]
@@ -37,7 +42,7 @@ def get(self, query)
 
     def set(self, results, query):
         """Set the result for the given query key in the cache.
-        
+
         When updating an entry, updates its position to the front of the LRU list.
         If the entry is new and the cache is at capacity, removes the oldest entry
         before the new entry is added.
@@ -58,4 +63,4 @@ def set(self, results, query):
             # Add the new key and value
             new_node = Node(results)
             self.linked_list.append_to_front(new_node)
-            self.lookup[query] = new_node
+            self.lookup[query] = new_node

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 remove_user(self, user_id):  # ...
-    def add_friend_request(self, from_user_id, to_user_id):  # ...
-    def approve_friend_request(self, from_user_id, to_user_id):  # ...
-    def reject_friend_request(self, from_user_id, to_user_id):  # ...
+    def add_user(self, user_id, name, pass_hash):
+        pass
+
+    def remove_user(self, 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 @@ def __init__(self, user_id, name, pass_hash):
         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_group(self, group_id, message):  # ...
-    def send_friend_request(self, friend_id):  # ...
-    def receive_friend_request(self, friend_id):  # ...
-    def approve_friend_request(self, friend_id):  # ...
-    def reject_friend_request(self, friend_id):  # ...
+    def message_user(self, friend_id, message):
+        pass
+
+    def message_group(self, group_id, message):
+        pass
+
+    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 @@ def __init__(self, first_user, second_user):
 
 class GroupChat(Chat):
 
-    def add_user(self, user):  # ...
-    def remove_user(self, user):  # ... 
+    def add_user(self, user):
+        pass
+
+    def remove_user(self, user):
+        pass
 
 
 class Message(object):
@@ -77,4 +100,4 @@ class RequestStatus(Enum):
     UNREAD = 0
     READ = 1
     ACCEPTED = 2
-    REJECTED = 3
+    REJECTED = 3

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 @@ def park_vehicle(self, vehicle):
 
     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 @@ def can_fit_vehicle(self, vehicle):
             return False
         return vehicle.can_fit_in_spot(self)
 
-    def park_vehicle(self, vehicle):  # ...
-    def remove_vehicle(self):  # ...
+    def park_vehicle(self, vehicle):
+        pass
+
+    def remove_vehicle(self):
+        pass

solutions/system_design/social_graph/social_graph_snippets.py

@@ -61,3 +61,4 @@ def __init__(self, person_ids, lookup):
     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 @@ def __init__(self, url, contents, child_urls):
 
     def create_signature(self):
         # Create signature based on url and contents
-        ...
+        pass
 
 
 class Crawler(object):