Merge pull request #297 from maheshgudi/difflib

StdIO error output simplification

15 files changed, 299 insertions, 104 deletions

diff --git a/yaksh/compare_stdio.py b/yaksh/compare_stdio.py
new file mode 100644
index 0000000..c4076de
--- /dev/null
+++ b/yaksh/compare_stdio.py
@@ -0,0 +1,43 @@
+try:
+    from itertools import zip_longest
+except ImportError:
+    from itertools import izip_longest as zip_longest
+
+    
+def _get_incorrect_user_lines(exp_lines, user_lines):
+    err_line_numbers = []
+    for line_no, (expected_line, user_line) in \
+     enumerate(zip_longest(exp_lines, user_lines)):
+        if not user_line or not expected_line or \
+         user_line.strip() != expected_line.strip():
+            err_line_numbers.append(line_no)
+    return err_line_numbers
+    
+def compare_outputs(expected_output, user_output, given_input=None):
+    given_lines = user_output.splitlines()
+    exp_lines = expected_output.splitlines()
+    msg = {"given_input":given_input,
+           "expected_output": exp_lines,
+           "user_output":given_lines
+            }
+    ng = len(given_lines)
+    ne = len(exp_lines)
+    err_line_numbers = _get_incorrect_user_lines(exp_lines, given_lines)
+    msg["error_line_numbers"] = err_line_numbers
+    if ng != ne:
+        msg["error_msg"] = ("Incorrect Answer: "
+                            + "We had expected {} number of lines. ".format(ne)
+                            + "We got {} number of lines.".format(ng)
+                            )
+        return False, msg
+    else:
+        if err_line_numbers:
+            msg["error_msg"] = ("Incorrect Answer: "
+                             + "Line number(s) {0} did not match."
+                                .format(", ".join(map(
+                                  str,[x+1 for x in err_line_numbers]
+                                ))))
+            return False, msg
+        else:
+            msg["error_msg"] = "Correct Answer"
+            return True, msg
diff --git a/yaksh/evaluator_tests/test_bash_evaluation.py b/yaksh/evaluator_tests/test_bash_evaluation.py
index 8bb8c81..6e7410e 100644
--- a/yaksh/evaluator_tests/test_bash_evaluation.py
+++ b/yaksh/evaluator_tests/test_bash_evaluation.py
@@ -242,7 +242,8 @@ class BashStdIOEvaluationTestCases(EvaluatorBaseTest):
         result = grader.evaluate(kwargs)
 
         # Then
-        self.assert_correct_output("Incorrect", result.get('error'))
+        result_error = result.get('error')[0].get('error_msg')
+        self.assert_correct_output("Incorrect", result_error)
         self.assertFalse(result.get('success'))
 
     def test_stdout_only(self):
diff --git a/yaksh/evaluator_tests/test_c_cpp_evaluation.py b/yaksh/evaluator_tests/test_c_cpp_evaluation.py
index b15f766..5ff4e4c 100644
--- a/yaksh/evaluator_tests/test_c_cpp_evaluation.py
+++ b/yaksh/evaluator_tests/test_c_cpp_evaluation.py
@@ -350,10 +350,11 @@ class CppStdIOEvaluationTestCases(EvaluatorBaseTest):
         result = grader.evaluate(kwargs)
 
         # Then
-        lines_of_error = len(result.get('error')[0].splitlines())
+        lines_of_error = len(result.get('error')[0].get('error_line_numbers'))
+        result_error = result.get('error')[0].get('error_msg')
         self.assertFalse(result.get('success'))
-        self.assert_correct_output("Incorrect", result.get('error'))
-        self.assertTrue(lines_of_error > 1)
+        self.assert_correct_output("Incorrect", result_error)
+        self.assertTrue(lines_of_error > 0)
 
     def test_error(self):
         # Given
@@ -558,10 +559,11 @@ class CppStdIOEvaluationTestCases(EvaluatorBaseTest):
         result = grader.evaluate(kwargs)
 
         # Then
-        lines_of_error = len(result.get('error')[0].splitlines())
+        lines_of_error = len(result.get('error')[0].get('error_line_numbers'))
+        result_error = result.get('error')[0].get('error_msg')
         self.assertFalse(result.get('success'))
-        self.assert_correct_output("Incorrect", result.get('error'))
-        self.assertTrue(lines_of_error > 1)
+        self.assert_correct_output("Incorrect", result_error)
+        self.assertTrue(lines_of_error > 0)
 
     def test_cpp_error(self):
         # Given
diff --git a/yaksh/evaluator_tests/test_java_evaluation.py b/yaksh/evaluator_tests/test_java_evaluation.py
index ea558ed..c733586 100644
--- a/yaksh/evaluator_tests/test_java_evaluation.py
+++ b/yaksh/evaluator_tests/test_java_evaluation.py
@@ -349,10 +349,11 @@ class JavaStdIOEvaluationTestCases(EvaluatorBaseTest):
         result = grader.evaluate(kwargs)
 
         # Then
-        lines_of_error = len(result.get('error')[0].splitlines())
+        lines_of_error = len(result.get('error')[0].get('error_line_numbers'))
+        result_error = result.get('error')[0].get('error_msg')
         self.assertFalse(result.get('success'))
-        self.assert_correct_output("Incorrect", result.get('error'))
-        self.assertTrue(lines_of_error > 1)
+        self.assert_correct_output("Incorrect", result_error)
+        self.assertTrue(lines_of_error > 0)
 
     def test_error(self):
         # Given
diff --git a/yaksh/evaluator_tests/test_python_evaluation.py b/yaksh/evaluator_tests/test_python_evaluation.py
index a751c40..a2faf77 100644
--- a/yaksh/evaluator_tests/test_python_evaluation.py
+++ b/yaksh/evaluator_tests/test_python_evaluation.py
@@ -613,8 +613,8 @@ class PythonStdIOEvaluationTestCases(EvaluatorBaseTest):
         # Then
         self.assertFalse(result.get('success'))
         self.assert_correct_output(
-            "ERROR:\nExpected:\n3\nGiven:\n-1\n\nError in line 1 of output.",
-            result.get('error')
+            "Incorrect Answer: Line number(s) 1 did not match.",
+            result.get('error')[0].get('error_msg')
         )
 
     def test_file_based_answer(self):
diff --git a/yaksh/evaluator_tests/test_python_stdio_evaluator.py b/yaksh/evaluator_tests/test_python_stdio_evaluator.py
index db5028a..8877544 100644
--- a/yaksh/evaluator_tests/test_python_stdio_evaluator.py
+++ b/yaksh/evaluator_tests/test_python_stdio_evaluator.py
@@ -1,7 +1,4 @@
-from textwrap import dedent
-
-from yaksh.python_stdio_evaluator import compare_outputs
-
+from yaksh.compare_stdio import compare_outputs
 
 def test_compare_outputs():
     exp = "5\n5\n"
@@ -27,36 +24,16 @@ def test_compare_outputs():
     exp = "5\n5\n"
     given = "5 5"
     success, msg = compare_outputs(given, exp)
+    error_msg = msg.get('error_msg')
     assert not success
-    m = dedent("""\
-    ERROR: Got 1 lines in output, we expected 2.
-    Expected:
-    5
-    5
-
-    Given:
-    5 5
-    """)
-    assert m == msg
+    m = ("Incorrect Answer: We had expected 1 number of lines. "
+          + "We got 2 number of lines.")
+    assert m == error_msg
 
     exp = "5\n5\n"
     given = "5\n6"
     success, msg = compare_outputs(given, exp)
+    error_msg = msg.get('error_msg')
+    m = "Incorrect Answer: Line number(s) 2 did not match."
     assert not success
-    m = dedent("""\
-    ERROR:
-    Expected:
-    5
-    5
-
-    Given:
-    5
-    6
-
-    Error in line 2 of output.
-    Expected line 2:
-    5
-    Given line 2:
-    6
-    """)
-    assert m == msg
+    assert m == error_msg
diff --git a/yaksh/python_stdio_evaluator.py b/yaksh/python_stdio_evaluator.py
index a8c797d..2b443a7 100644
--- a/yaksh/python_stdio_evaluator.py
+++ b/yaksh/python_stdio_evaluator.py
@@ -1,7 +1,6 @@
 import sys
 from contextlib import contextmanager
 
-
 try:
     from StringIO import StringIO
 except ImportError:
@@ -10,6 +9,7 @@ except ImportError:
 # Local imports
 from .file_utils import copy_files, delete_files
 from .base_evaluator import BaseEvaluator
+from .compare_stdio import compare_outputs
 
 
 @contextmanager
@@ -21,37 +21,6 @@ def redirect_stdout():
     finally:
         sys.stdout = old_target  # restore to the previous value
 
-
-def _show_expected_given(expected, given):
-    return "Expected:\n{0}\nGiven:\n{1}\n".format(expected, given)
-
-
-def compare_outputs(given, expected):
-    given_lines = given.splitlines()
-    ng = len(given_lines)
-    exp_lines = expected.splitlines()
-    ne = len(exp_lines)
-    if ng != ne:
-        msg = "ERROR: Got {0} lines in output, we expected {1}.\n".format(
-            ng, ne
-        )
-        msg += _show_expected_given(expected, given)
-        return False, msg
-    else:
-        for i, (given_line, expected_line) in \
-           enumerate(zip(given_lines, exp_lines)):
-            if given_line.strip() != expected_line.strip():
-                msg = "ERROR:\n"
-                msg += _show_expected_given(expected, given)
-                msg += "\nError in line %d of output.\n" % (i+1)
-                msg += "Expected line {0}:\n{1}\nGiven line {0}:\n{2}\n"\
-                       .format(
-                           i+1, expected_line, given_line
-                       )
-                return False, msg
-    return True, "Correct answer."
-
-
 class PythonStdIOEvaluator(BaseEvaluator):
     """Tests the Python code obtained from Code Server"""
     def __init__(self, metadata, test_case_data):
@@ -77,6 +46,7 @@ class PythonStdIOEvaluator(BaseEvaluator):
             self.files = copy_files(self.file_paths)
         submitted = compile(self.user_answer, '<string>', mode='exec')
         if self.expected_input:
+            self.expected_input = self.expected_input.replace('\r', '')
             input_buffer = StringIO()
             input_buffer.write(self.expected_input)
             input_buffer.seek(0)
@@ -89,5 +59,8 @@ class PythonStdIOEvaluator(BaseEvaluator):
 
     def check_code(self):
         mark_fraction = self.weight
-        success, err = compare_outputs(self.output_value, self.expected_output)
+        success, err = compare_outputs(self.expected_output,
+                                       self.output_value,
+                                       self.expected_input
+                                       )
         return success, err, mark_fraction
diff --git a/yaksh/static/yaksh/css/exam.css b/yaksh/static/yaksh/css/exam.css
new file mode 100644
index 0000000..fff904e
--- /dev/null
+++ b/yaksh/static/yaksh/css/exam.css
@@ -0,0 +1,7 @@
+table td, table th { border: black solid 1px !important;
+			word-wrap: break-word !important;
+			white-space: pre-wrap !important;
+			}
+output{
+	table-layout: fixed
+}
\ No newline at end of file
diff --git a/yaksh/stdio_evaluator.py b/yaksh/stdio_evaluator.py
index 554d4c5..932ae7e 100644
--- a/yaksh/stdio_evaluator.py
+++ b/yaksh/stdio_evaluator.py
@@ -5,6 +5,7 @@ import signal
 # Local imports
 from .base_evaluator import BaseEvaluator
 from .grader import TimeoutException
+from .compare_stdio import compare_outputs
 
 
 class StdIOEvaluator(BaseEvaluator):
@@ -20,18 +21,8 @@ class StdIOEvaluator(BaseEvaluator):
             os.killpg(os.getpgid(proc.pid), signal.SIGTERM)
             raise
         expected_output = expected_output.replace("\r", "")
-        if not expected_input:
-            error_msg = "Expected Output is\n{0} ".\
-                        format(str(expected_output))
-        else:
-            error_msg = "Given Input is\n{0}\nExpected Output is\n{1}".\
-                        format(expected_input, str(expected_output))
-        if output_err == '':
-            if user_output == expected_output:
-                success, err = True, None
-            else:
-                err = "Incorrect answer:\n" + error_msg +\
-                      "\nYour output is\n{0}".format(str(user_output))
-        else:
-            err = "Error:\n{0}".format(output_err)
+        success, err = compare_outputs(expected_output,
+                                       user_output,
+                                       expected_input
+                                       )
         return success, err
diff --git a/yaksh/templates/exam.html b/yaksh/templates/exam.html
index a18a962..45b85f0 100644
--- a/yaksh/templates/exam.html
+++ b/yaksh/templates/exam.html
@@ -1,4 +1,5 @@
 {% extends "base.html" %}
+{% load custom_filters %}
 {% block css%}
     <link rel="stylesheet" href="{{ URL_ROOT }}/static/yaksh/css/dashboard.css" type="text/css" />
 {% endblock %}
@@ -77,13 +78,56 @@
                 {% if error_message %}
                     <div class="row" id="error_panel">
       {% for error in error_message %}
-      {% if error == "Correct answer" %}
-              <div class="panel panel-success">
-          {% else %}
               <div class="panel panel-danger">
-          {% endif %}
       <div class="panel-heading">Testcase No. {{ forloop.counter }}</div>
-      <div class="panel-body"><pre><code>{{ error }}</code></pre></div>
+      <div class="panel-body">
+      <div class="well well-sm">
+      {% if not error.expected_output %}
+      <pre><code> {{error|safe}} </code></pre>
+      {% else %}
+        {% if error.given_input %}
+       <table class="table table-bordered">
+        <col width="30%">
+          <tr class = "active">
+          <td> For given Input value(s):</td>
+          <td>{{error.given_input}}</td>
+          </tr>
+       </table>
+       {% endif %}
+        <table class="table table-bordered" width="100%" id="output">
+          <col width="10%">
+          <col width="40%">
+          <col width="40%">
+          <col width="10%">
+          <tr class="info">
+          <th><center>Line No.</center></th>
+          <th><center>Expected Output</center></th>
+          <th><center>User output</center></th>
+          <th><center>Status</center></th>
+          </tr>
+          {% for expected,user in error.expected_output|zip:error.user_output %}
+          <td> {{forloop.counter}} </td>
+          <td>{{expected|default:""}} </td>
+          <td>{{user|default:""}}</td>
+          {% if forloop.counter0 in error.error_line_numbers or not expected or not user %}
+          <td><span class ="glyphicon glyphicon-remove text-warning"/></td>
+          {% else %}
+          <td><span class ="glyphicon glyphicon-ok text-success"/></td>
+          {% endif %}
+          </tr>
+          {% endfor %}
+          </table>
+          <table width="100%" class='table table-bordered'>
+          <col width="10">
+          <tr class = "danger">
+          <td><b>Error:</b></td>
+           <td>{{error.error_msg}}</td>
+           </tr>
+          </table>
+        
+        {% endif %}
+        </div>
+      </div>
       </div>
       {% endfor %}
 
diff --git a/yaksh/templates/yaksh/grade_user.html b/yaksh/templates/yaksh/grade_user.html
index c93ec10..9cdfb1a 100644
--- a/yaksh/templates/yaksh/grade_user.html
+++ b/yaksh/templates/yaksh/grade_user.html
@@ -1,4 +1,5 @@
 {% extends "manage.html" %}
+{% load custom_filters %}
 
 {% block title %} Grade User {% endblock %}
 
@@ -132,6 +133,7 @@ Status : <b style="color: green;"> Passed </b><br/>
 {% csrf_token %}
 
 {% for question, answers in paper.get_question_answers.items %}
+<div class = "well well-sm">
 <div class="panel panel-info">
         <div class="panel-heading">
             <strong> Details: {{forloop.counter}}. {{ question.summary }} 
@@ -198,10 +200,57 @@ Status : <b style="color: green;"> Passed </b><br/>
                 <div class="panel panel-danger">
                     <div class="panel-heading">Error:
             {% endif %}
-            {% for err in ans.error_list %}
-                <div><pre>{{ err }}</pre></div>
-            {% endfor %}
+            {% with ans.error_list as err %}
+            {% for error in err %}
+            {% if not error.expected_output %}
+      <pre><code> {{error|safe}} </code></pre>
+      {% else %}
+        <div class = "well well-sm">
+        {% if error.given_input %}
+       <table class="table table-bordered">
+        <col width="30%">
+          <tr class = "active">
+          <td> For given Input value(s):</td>
+          <td>{{error.given_input}}</td>
+          </tr>
+       </table>
+       {% endif %}
+        <table class="table table-bordered" width="100%" id="output">
+          <col width="10%">
+          <col width="40%">
+          <col width="40%">
+          <col width="10%">
+          <tr class="info">
+          <th><center>Line No.</center></th>
+          <th><center>Expected Output</center></th>
+          <th><center>User output</center></th>
+          <th><center>Status</center></th>
+          </tr>
+          {% for expected,user in error.expected_output|zip:error.user_output %}
+          <td> {{forloop.counter}} </td>
+          <td>{{expected|default:""}} </td>
+          <td>{{user|default:""}}</td>
+          {% if forloop.counter0 in error.error_line_numbers or not expected or not user %}
+          <td><span class ="glyphicon glyphicon-remove text-warning"/></td>
+          {% else %}
+          <td><span class ="glyphicon glyphicon-ok text-success"/></td>
+          {% endif %}
+          </tr>
+          {% endfor %}
+          </table>
+          <table width="100%" class='table table-bordered'>
+          <col width="10">
+          <tr class = "danger">
+          <td><b>Error:</b></td>
+           <td>{{error.error_msg}}</td>
+           </tr>
+          </table>
         </div>
+        {% endif %}
+        {% endfor %}
+        {% endwith %}
+        </div>
+        
         <div class="panel-body">
         {% if question.type != "code" %}
         <div class="well well-sm">
@@ -220,6 +269,7 @@ Status : <b style="color: green;"> Passed </b><br/>
         value="{{ answer.answer.marks }}"><br><br>
     {% endwith %}
     <hr/>
+    </div>
     {% endfor %} {# for question, answers ... #}
 <div class="form-group">
 <h3>Teacher comments: </h3>
@@ -233,6 +283,7 @@ Status : <b style="color: green;"> Passed </b><br/>
 
 {% endif %} {# if paper.answers.count #}
 
+
 {% endfor %} {# for paper in data.papers #}
 
 {% endif %} {#  if data.papers #}
diff --git a/yaksh/templates/yaksh/question.html b/yaksh/templates/yaksh/question.html
index 0dad59d..ee33523 100644
--- a/yaksh/templates/yaksh/question.html
+++ b/yaksh/templates/yaksh/question.html
@@ -6,6 +6,7 @@
 <link rel="stylesheet" href="{{ URL_ROOT }}/static/yaksh/css/dashboard.css" type="text/css" />
 <link rel="stylesheet" href="{{ URL_ROOT }}/static/yaksh/css/question.css" type="text/css" />
 <link rel="stylesheet" href="{{ URL_ROOT }}/static/yaksh/css/codemirror/lib/codemirror.css" type="text/css" />
+<link rel="stylesheet" href="{{ URL_ROOT }}/static/yaksh/css/exam.css" type="text/css" />
 <style>
     .CodeMirror{
         border-style: groove;
@@ -238,7 +239,7 @@ function call_skip(url)
         <div class="from-group">
 
          {% if question.type == "mcq" or "mcc" or "integer" or "float" or "string" %}
-         <br><button class="btn btn-primary" type="submit" name="check" id="check">Submit Answer</button>&nbsp;&nbsp;
+         <br><button class="btn btn-primary" type="submit" name="check" id="check">Submit Answer</button>&nbsp;&nbsp;<br/>
          {% elif question.type == "upload" %}
          <br><button class="btn btn-primary" type="submit" name="check" id="check" onClick="return validate();">Upload</button>&nbsp;&nbsp;
 
diff --git a/yaksh/templates/yaksh/user_data.html b/yaksh/templates/yaksh/user_data.html
index 6e62b66..a8adc22 100644
--- a/yaksh/templates/yaksh/user_data.html
+++ b/yaksh/templates/yaksh/user_data.html
@@ -1,4 +1,5 @@
 {% extends "manage.html" %}
+{% load custom_filters %}
 
 {% block pagetitle %} Data for user {{ data.user.get_full_name.title }} {% endblock pagetitle %}
 
@@ -118,11 +119,56 @@ User IP address: {{ paper.user_ip }}
         {% else %}
             <div class="panel panel-danger">
             <div class="panel-heading">Error
-        
-        {% for error in answer.error_list %}
-        <div><pre><code>{{ error }}</code></pre></div>
+        {% with answer.error_list as err %}
+            {% for error in err %}
+            {% if not error.expected_output %}
+      <pre><code> {{error|safe}} </code></pre>
+      {% else %}
+        <div class = "well well-sm">
+        {% if error.given_input %}
+       <table class="table table-bordered">
+        <col width="30%">
+          <tr class = "active">
+          <td> For given Input value(s):</td>
+          <td>{{error.given_input}}</td>
+          </tr>
+       </table>
+       {% endif %}
+        <table class="table table-bordered" width="100%" id="output">
+          <col width="10%">
+          <col width="40%">
+          <col width="40%">
+          <col width="10%">
+          <tr class="info">
+          <th><center>Line No.</center></th>
+          <th><center>Expected Output</center></th>
+          <th><center>User output</center></th>
+          <th><center>Status</center></th>
+          </tr>
+          {% for expected,user in error.expected_output|zip:error.user_output %}
+          <td> {{forloop.counter}} </td>
+          <td>{{expected|default:""}} </td>
+          <td>{{user|default:""}}</td>
+          {% if forloop.counter0 in error.error_line_numbers or not expected or not user %}
+          <td><span class ="glyphicon glyphicon-remove text-warning"/></td>
+          {% else %}
+          <td><span class ="glyphicon glyphicon-ok text-success"/></td>
+          {% endif %}
+          </tr>
+          {% endfor %}
+          </table>
+          <table width="100%" class='table table-bordered'>
+          <col width="10">
+          <tr class = "danger">
+          <td><b>Error:</b></td>
+           <td>{{error.error_msg}}</td>
+           </tr>
+          </table>
+        </div>
+        {% endif %}
         {% endfor %}
-        {% endif %}    
+        {% endwith %}
+        {% endif %}
     
     </div>
     <div class="panel-body">
diff --git a/yaksh/templates/yaksh/view_answerpaper.html b/yaksh/templates/yaksh/view_answerpaper.html
index f4c8846..9edff5a 100644
--- a/yaksh/templates/yaksh/view_answerpaper.html
+++ b/yaksh/templates/yaksh/view_answerpaper.html
@@ -1,4 +1,5 @@
 {% extends "user.html" %}
+{% load custom_filters %}
 
 {% block pagetitle %} Answer Paper  for {{ quiz.description }}{% endblock pagetitle %}
 
@@ -102,7 +103,56 @@
         {% else %}
             <div class="panel panel-danger">
         {% endif %}
-    <div class="panel-heading">Autocheck: {{ answer.error }}</div>
+    <div class="panel-heading">Error:</div>
+        {% with answer.error_list as err %}
+            {% for error in err %}
+            {% if not error.expected_output %}
+      <pre><code> {{error|safe}} </code></pre>
+      {% else %}
+        <div class = "well well-sm">
+        {% if error.given_input %}
+       <table class="table table-bordered">
+        <col width="30%">
+          <tr class = "active">
+          <td> For given Input value(s):</td>
+          <td>{{error.given_input}}</td>
+          </tr>
+       </table>
+       {% endif %}
+        <table class="table table-bordered" width="100%" id="output">
+          <col width="10%">
+          <col width="40%">
+          <col width="40%">
+          <col width="10%">
+          <tr class="info">
+          <th><center>Line No.</center></th>
+          <th><center>Expected Output</center></th>
+          <th><center>User output</center></th>
+          <th><center>Status</center></th>
+          </tr>
+          {% for expected,user in error.expected_output|zip:error.user_output %}
+          <td> {{forloop.counter}} </td>
+          <td>{{expected|default:""}} </td>
+          <td>{{user|default:""}}</td>
+          {% if forloop.counter0 in error.error_line_numbers or not expected or not user %}
+          <td><span class ="glyphicon glyphicon-remove text-warning"/></td>
+          {% else %}
+          <td><span class ="glyphicon glyphicon-ok text-success"/></td>
+          {% endif %}
+          </tr>
+          {% endfor %}
+          </table>
+          <table width="100%" class='table table-bordered'>
+          <col width="10">
+          <tr class = "danger">
+          <td><b>Error:</b></td>
+           <td>{{error.error_msg}}</td>
+           </tr>
+          </table>
+        </div>
+        {% endif %}
+        {% endfor %}
+        {% endwith %}
     <div class="panel-body">
     <pre><code>{{ answer.answer.answer.strip }}</code></pre>
     </div>
diff --git a/yaksh/templatetags/custom_filters.py b/yaksh/templatetags/custom_filters.py
index f610cc6..df6ecce 100644
--- a/yaksh/templatetags/custom_filters.py
+++ b/yaksh/templatetags/custom_filters.py
@@ -1,5 +1,9 @@
 from django import template
 from django.template.defaultfilters import stringfilter
+try:
+    from itertools import zip_longest
+except ImportError:
+    from itertools import izip_longest as zip_longest
 
 register = template.Library()
 
@@ -19,3 +23,7 @@ def completed(answerpaper):
 @register.assignment_tag(name="inprogress")
 def inprogress(answerpaper):
 	return answerpaper.filter(status="inprogress").count()
+
+@register.filter(name='zip')
+def zip_longest_out(a, b):
+	return zip_longest(a, b)