Added style #15. Does this clarify REST?

15-restful/README.md

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+Style #15
+==============================
+
+REST = REpresentational State Transfer (http://www.ics.uci.edu/~fielding/pubs/dissertation/top.htm)
+
+REST is a style for network-based interactive applications that
+underlies the Web. The example here doesn't go over the network, but
+preserves the main contraints of REST, which are:
+
+- Interactive: end-to-end between an active agent (e.g. a person) and a backend
+
+- Separation between Client (user interface) and Server (data storage)
+
+- Statelessness, as in client--stateless-server: every request from
+  client to server must contain all the information necessary for the
+  server to serve the request. The server cannot store
+  context of the interaction. Session state is on the client.
+
+- Uniform interface: resources that are created and retrieved,
+  resource identifiers and hypermedia representation that is the
+  engine of application state
+
+Additionally, the networked style has the following contraints, not shown here:
+
+- Cache
+
+- Layered system
+
+- Code-on-demans
+
+Possible names:
+
+- RESTful
+- Stateless Ping-Pong
+

15-restful/tf-15.py

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+import re, string, sys
+
+with open("../stop_words.txt") as f:
+    stops = set(f.read().split(",") + list(string.ascii_lowercase))
+# The "database"
+data = {}
+
+# Internal functions of the "server"-side application
+def error_state():
+    return "Something wrong", ["get", "default", None]
+
+# The "server"-side application handlers
+def quit_handler(args):
+    sys.exit("Goodbye cruel world...")
+
+def default_get_handler(args):
+        rep = "What would you like to do?"
+        rep += "\n1 - Quit" + "\n2 - Upload file"
+        links = {"1" : ["post", "execution", None], "2" : ["get", "file_form", None]}
+        return rep, links
+
+def upload_get_handler(args):
+    return "Name of file to upload?", ["post", "file"]
+        
+def upload_post_handler(args):
+    def create_data(filename):
+        if filename in data:
+            return
+        word_freqs = {}
+        print "Trying to open " + filename
+        with open(filename) as f:
+            for w in [x.lower() for x in re.split("[^a-zA-Z]+", f.read()) if len(x) > 0 and x.lower() not in stops]:
+                word_freqs[w] = word_freqs.get(w, 0) + 1
+        word_freqsl = word_freqs.items()
+        word_freqsl.sort(lambda x, y: cmp(y[1], x[1]))
+        data[filename] = word_freqsl
+
+    if args == None:
+        return error_state()
+
+    filename = args[0]
+    try:
+        create_data(filename)
+    except:
+        return error_state()
+
+    return word_get_handler([filename, 0])
+
+def word_get_handler(args):
+    def get_word(filename, word_index):
+        if word_index < len(data[filename]):
+            return data[filename][word_index]
+        else:
+            return ("no more words", 0) 
+
+    filename = args[0]; word_index = args[1]
+    word_info = get_word(filename, word_index)
+    rep = '\n#{0}: {1} - {2}'.format(word_index+1, word_info[0], word_info[1])
+    rep += "\n\nWhat would you like to do next?"
+    rep += "\n1 - Quit" + "\n2 - Upload file"
+    rep += "\n3 - See next most-frequently occurring word"
+    links = {"1" : ["post", "execution", None], 
+             "2" : ["get", "file_form", None], 
+             "3" : ["get", "word", [filename, word_index+1]]}
+    return rep, links
+
+# Handler registration
+handlers = {"post_execution" : quit_handler,
+            "get_default" : default_get_handler, 
+            "get_file_form" : upload_get_handler, 
+            "post_file" : upload_post_handler, 
+            "get_word" : word_get_handler }
+
+# The "server" core
+def handle_request(verb, uri, args):
+    def handler_key(verb, uri):
+        return verb + "_" + uri
+
+    if handler_key(verb, uri) in handlers:
+        return handlers[handler_key(verb, uri)](args)
+    else:
+        return handlers[handler_key("get", "default")](args)
+
+# A very simple client "browser"
+def render_and_get_input(state_representation, links):
+    print state_representation
+    if type(links) is dict: # many possible next states
+        input = sys.stdin.readline().strip()
+        if input in links:
+            return links[input]
+        else:
+            return ["get", "default", None]
+    elif type(links) is list: # only one possible next state
+        if links[0] == "post": # get "form" data
+            input = sys.stdin.readline().strip()
+            links.append([input]) # add the data at the end
+            return links
+        else: # get action, don't get user input
+            return links
+    else:
+        return ["get", "default", None]
+
+request = ["get", "default", None]
+while True:
+    # "server"-side computation
+    state_representation, links = handle_request(*request)
+    # "client"-side computation
+    request = render_and_get_input(state_representation, links)