Renaming item to only_one, and adding documentation

common/lib/xmodule/capa_module.py

@@ -18,7 +18,12 @@ log = logging.getLogger("mitx.courseware")
 TIMEDELTA_REGEX = re.compile(r'^((?P<days>\d+?) day(?:s?))?(\s)?((?P<hours>\d+?) hour(?:s?))?(\s)?((?P<minutes>\d+?) minute(?:s)?)?(\s)?((?P<seconds>\d+?) second(?:s)?)?$')
 
 
-def item(l, default="", process=lambda x: x):
+def only_one(lst, default="", process=lambda x: x):
+    """
+    If lst is empty, returns default
+    If lst has a single element, applies process to that element and returns it
+    Otherwise, raises an exeception
+    """
     if len(l) == 0:
         return default
     elif len(l) == 1:
@@ -163,18 +168,18 @@ class Module(XModule):
 
         dom2 = etree.fromstring(xml)
 
-        self.explanation = "problems/" + item(dom2.xpath('/problem/@explain'), default="closed")
-        # TODO: Should be converted to: self.explanation=item(dom2.xpath('/problem/@explain'), default="closed")
-        self.explain_available = item(dom2.xpath('/problem/@explain_available'))
+        self.explanation = "problems/" + only_one(dom2.xpath('/problem/@explain'), default="closed")
+        # TODO: Should be converted to: self.explanation=only_one(dom2.xpath('/problem/@explain'), default="closed")
+        self.explain_available = only_one(dom2.xpath('/problem/@explain_available'))
 
-        display_due_date_string = item(dom2.xpath('/problem/@due'))
+        display_due_date_string = only_one(dom2.xpath('/problem/@due'))
         if len(display_due_date_string) > 0:
             self.display_due_date = dateutil.parser.parse(display_due_date_string)
             #log.debug("Parsed " + display_due_date_string + " to " + str(self.display_due_date))
         else:
             self.display_due_date = None
 
-        grace_period_string = item(dom2.xpath('/problem/@graceperiod'))
+        grace_period_string = only_one(dom2.xpath('/problem/@graceperiod'))
         if len(grace_period_string) >0 and self.display_due_date:
             self.grace_period = parse_timedelta(grace_period_string)
             self.close_date = self.display_due_date + self.grace_period
@@ -183,18 +188,18 @@ class Module(XModule):
             self.grace_period = None
             self.close_date = self.display_due_date
 
-        self.max_attempts =item(dom2.xpath('/problem/@attempts'))
+        self.max_attempts =only_one(dom2.xpath('/problem/@attempts'))
         if len(self.max_attempts)>0:
             self.max_attempts =int(self.max_attempts)
         else:
             self.max_attempts =None
 
-        self.show_answer =item(dom2.xpath('/problem/@showanswer'))
+        self.show_answer =only_one(dom2.xpath('/problem/@showanswer'))
 
         if self.show_answer =="":
             self.show_answer ="closed"
 
-        self.rerandomize =item(dom2.xpath('/problem/@rerandomize'))
+        self.rerandomize =only_one(dom2.xpath('/problem/@rerandomize'))
         if self.rerandomize =="" or self.rerandomize=="always" or self.rerandomize=="true":
             self.rerandomize="always"
         elif self.rerandomize=="false" or self.rerandomize=="per_student":
@@ -209,10 +214,10 @@ class Module(XModule):
         if state!=None and 'attempts' in state:
             self.attempts=state['attempts']
 
-        # TODO: Should be: self.filename=item(dom2.xpath('/problem/@filename'))
-        self.filename= "problems/"+item(dom2.xpath('/problem/@filename'))+".xml"
-        self.name=item(dom2.xpath('/problem/@name'))
-        self.weight=item(dom2.xpath('/problem/@weight'))
+        # TODO: Should be: self.filename=only_one(dom2.xpath('/problem/@filename'))
+        self.filename= "problems/"+only_one(dom2.xpath('/problem/@filename'))+".xml"
+        self.name=only_one(dom2.xpath('/problem/@name'))
+        self.weight=only_one(dom2.xpath('/problem/@weight'))
         if self.rerandomize == 'never':
             seed = 1
         else: