prolog.engine: use .get() to access reply

In case SWI engine goes insane and returns a malformed reply (has
happened). Also fix the test case in this file to use the new, classless
methods.

1 files changed, 17 insertions, 16 deletions

diff --git a/prolog/engine.py b/prolog/engine.py
index af79535..e64f728 100644
--- a/prolog/engine.py
+++ b/prolog/engine.py
@@ -6,22 +6,24 @@ import json
 import re
 import urllib
 
-# Create a new pengine. If query is given: run it, destroy the engine and
-# return the reply. Otherwise, return the ID of the new pengine.
+# Create a new pengine, initialize it with [code] and return its ID. The engine
+# will be destroyed after completing one query.
 def create(code=''):
     opts = {'format': 'json-s', 'destroy': True, 'src_text': code}
     reply, messages = request('POST', '/pengine/create', body=json.dumps(opts))
 
-    if reply['event'] != 'create' or 'error' in messages:
+    if reply.get('event') != 'create' or 'error' in messages:
         raise Exception('\n'.join(messages['error']))
 
     return reply['id']
 
+# Create a new pengine with [code], run [query] and destroy the engine. Return
+# the reply from engine.
 def create_and_ask(code, query):
     opts = {'format': 'json-s', 'destroy': True, 'src_text': code, 'ask': query}
     reply, messages = request('POST', '/pengine/create', body=json.dumps(opts))
 
-    if reply['event'] != 'create' or 'error' in messages:
+    if reply.get('event') != 'create' or 'error' in messages:
         raise Exception('\n'.join(messages['error']))
 
     return reply['answer']['data']
@@ -60,7 +62,7 @@ def request(method, path, body=None):
                 raise Exception('server returned {}'.format(response.status))
 
             reply = json.loads(response.read().decode('utf-8'))
-            if reply['event'] == 'output':
+            if reply.get('event') == 'output':
                 msg_type, msg_data = get_message(reply)
                 messages[msg_type].append(msg_data)
 
@@ -90,15 +92,14 @@ def get_message(reply):
 
         if reply.get('code') == 'syntax_error':
             match = re.match(r'^.*Syntax error: (.*)$', data, flags=re.DOTALL)
-            message += match.group(1)
+            data = match.group(1)
         elif reply.get('code') == 'permission_error':
             match = re.match(r'^.*(No permission [^\n]*)', data, flags=re.DOTALL)
-            message += match.group(1)
+            data = match.group(1)
         elif reply.get('code') == 'type_error':
             match = re.match(r'^.*(Type error: [^\n]*)', data, flags=re.DOTALL)
-            message += match.group(1)
-        else:
-            message += data
+            data = match.group(1)
+        message += data
 
     # Replace anonymous variable names with _.
     message = re.sub(r'_G[0-9]*', '_', message)
@@ -109,7 +110,7 @@ def get_message(reply):
 def test_all(name, code):
     reply = create_and_ask(code=code, query="run_tests({}, Results)".format(name))
 
-    if reply['event'] != 'success':
+    if reply.get('event') != 'success':
         raise Exception('testing procedure failed')
 
     results = re.findall(r'(?:success|failure)\([^)]*\)', reply['data'][0]['Results'])
@@ -122,13 +123,13 @@ def test_all(name, code):
 def test(name, code):
     try:
         reply = create_and_ask(code=code, query='run_tests({})'.format(name))
-        return reply['event'] == 'success'
+        return reply.get('event') == 'success'
     except Exception as ex:
         return False
 
 # Basic sanity check.
 if __name__ == '__main__':
-    engine = PrologEngine(code='dup([],[]). dup([H|T],[H,H|TT]) :- dup(T,TT).')
-    print('engine id is ' + engine.id)
-    print(engine.ask("run_tests({}, Result)".format('dup/2')))
-    engine.destroy()
+    engine = create(code='dup([],[]). dup([H|T],[H,H|TT]) :- dup(T,TT).')
+    print('engine id is ' + engine)
+    print(ask(engine, "run_tests({}, Result)".format('dup/2')))
+    destroy(engine)