Inject MathJax JS to render math in locally-saved instructions

You still need the Internet to render math when you open instructions
later.

coursera/api.py

@@ -22,7 +22,7 @@ from .define import (OPENCOURSE_SUPPLEMENT_URL,
                      OPENCOURSE_ONDEMAND_COURSE_MATERIALS,
                      OPENCOURSE_VIDEO_URL,
 
-                     INSTRUCTIONS_CSS,
+                     INSTRUCTIONS_HTML_INJECTION,
 
                      IN_MEMORY_EXTENSION,
                      IN_MEMORY_MARKER)
@@ -173,7 +173,7 @@ class CourseraOnDemand(object):
         @type soup: BeautifulSoup
         """
         # 1. Inject basic CSS style
-        css_soup = BeautifulSoup(INSTRUCTIONS_CSS)
+        css_soup = BeautifulSoup(INSTRUCTIONS_HTML_INJECTION)
         soup.head.append(css_soup)
 
         # 2. Replace <text> with <p>

coursera/coursera_dl.py

@@ -53,6 +53,7 @@ import shutil
 import subprocess
 import sys
 import time
+import codecs
 
 from distutils.version import LooseVersion as V
 
@@ -313,7 +314,7 @@ def parse_on_demand_syllabus(session, page, reverse=False, intact_fnames=False,
     course_name = dom['slug']
 
     logging.info('Parsing syllabus of on-demand course. '
-                 'This may take some time, be patient ...')
+                 'This may take some time, please be patient ...')
     modules = []
     json_modules = dom['courseMaterial']['elements']
     course = CourseraOnDemand(session=session, course_id=dom['id'])
@@ -551,7 +552,7 @@ def download_lectures(downloader,
                     if not skip_download:
                         if url.startswith(IN_MEMORY_MARKER):
                             page_content = url[len(IN_MEMORY_MARKER):]
-                            with open(lecfn, 'w') as file_object:
+                            with codecs.open(lecfn, 'w', 'utf-8') as file_object:
                                 file_object.write(page_content)
                         elif:
                             if not url.startswith('mailto:'):

coursera/define.py

@@ -151,7 +151,7 @@ IN_MEMORY_EXTENSION = 'html'
 IN_MEMORY_MARKER = '#inmemory#'
 
 #: CSS that is usen to prettify instructions
-INSTRUCTIONS_CSS = '''
+INSTRUCTIONS_HTML_INJECTION = '''
 <style>
 pre {
     display: block;
@@ -165,4 +165,18 @@ pre {
     border: 1px solid #ccc;
 }
 </style>
+
+<script type="text/javascript" async
+  src="https://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML">
+</script>
+
+<script type="text/x-mathjax-config">
+  MathJax.Hub.Config({
+    tex2jax: {
+      inlineMath: [ ['$$','$$'], ['$','$'] ],
+      displayMath: [ ["\\\\[","\\\\]"] ],
+      processEscapes: true
+    }
+  });
+</script>
 '''