Make mistune a requirement for nbconvert

.travis.yml

@@ -16,8 +16,7 b' before_install:'
     - time sudo apt-get install pandoc casperjs nodejs libzmq3-dev
     # pin tornado < 4 for js tests while phantom is on super old webkit
     - if [[ $GROUP == 'js' ]]; then pip install 'tornado<4'; fi
-    - time pip install -f https://nipy.bic.berkeley.edu/wheelhouse/travis jinja2 sphinx pygments tornado requests mock pyzmq jsonschema jsonpointer
-    - time npm install -g requirejs jquery
+    - time pip install -f https://nipy.bic.berkeley.edu/wheelhouse/travis jinja2 sphinx pygments tornado requests mock pyzmq jsonschema jsonpointer mistune
 install:
     - time python setup.py install -q 
 script:

IPython/nbconvert/filters/markdown.py

@@ -18,13 +18,12 b' from __future__ import print_function'
 # Stdlib imports
 import os
 import subprocess
-import warnings
 from io import TextIOWrapper, BytesIO
 
-try:
-    import mistune
-except ImportError:
-    mistune = None
+import mistune
+from pygments import highlight
+from pygments.lexers import get_lexer_by_name
+from pygments.formatters import HtmlFormatter
 
 # IPython imports
 from IPython.nbconvert.utils.pandoc import pandoc
@@ -70,50 +69,37 b' def markdown2latex(source):'
     """
     return pandoc(source, 'markdown', 'latex')
 
-def markdown2html(source):
-    """Convert a markdown string to HTML"""
-    global _node
-    if _node is None:
-        # prefer md2html via marked if node.js >= 0.9.12 is available
-        # node is called nodejs on debian, so try that first
-        _node = 'nodejs'
-        if not _verify_node(_node):
-            _node = 'node'
-            if not _verify_node(_node):
-                warnings.warn(  "Node.js 0.9.12 or later wasn't found.\n" +
-                                "Nbconvert will try to use Pandoc instead.")
-                _node = False
-    if _node:
-        return markdown2html_marked(source)
-    if mistune is not None:
-        return markdown2html_mistune(source)
-    else:
-        return markdown2html_pandoc(source)
-
-if mistune is not None:
-    from pygments import highlight
-    from pygments.lexers import get_lexer_by_name
-    from pygments.formatters import HtmlFormatter
-
-    class MyRenderer(mistune.Renderer):
-        def block_code(self, code, lang):
-            if not lang:
-                return '\n<pre><code>%s</code></pre>\n' % \
-                    mistune.escape(code)
-            lexer = get_lexer_by_name(lang, stripall=True)
-            formatter = HtmlFormatter()
-            return highlight(code, lexer, formatter)
+
+class MyRenderer(mistune.Renderer):
+    def block_code(self, code, lang):
+        if not lang:
+            return '\n<pre><code>%s</code></pre>\n' % \
+                mistune.escape(code)
+        lexer = get_lexer_by_name(lang, stripall=True)
+        formatter = HtmlFormatter()
+        return highlight(code, lexer, formatter)
 
 def markdown2html_mistune(source):
+    """Convert a markdown string to HTML using mistune"""
     return mistune.Markdown(renderer=MyRenderer()).render(source)
 
 def markdown2html_pandoc(source):
     """Convert a markdown string to HTML via pandoc"""
     return pandoc(source, 'markdown', 'html', extra_args=['--mathjax'])
 
+def _find_nodejs():
+    global _node
+    if _node is None:
+        # prefer md2html via marked if node.js >= 0.9.12 is available
+        # node is called nodejs on debian, so try that first
+        _node = 'nodejs'
+        if not _verify_node(_node):
+            _node = 'node'
+    return _node
+
 def markdown2html_marked(source, encoding='utf-8'):
     """Convert a markdown string to HTML via marked"""
-    command = [_node, marked]
+    command = [_find_nodejs(), marked]
     try:
         p = subprocess.Popen(command,
                              stdin=subprocess.PIPE, stdout=subprocess.PIPE
@@ -127,6 +113,9 b" def markdown2html_marked(source, encoding='utf-8'):"
     out = TextIOWrapper(BytesIO(out), encoding, 'replace').read()
     return out.rstrip('\n')
 
+# The mistune renderer is the default, because it's simple to depend on it
+markdown2html = markdown2html_mistune
+
 def markdown2rst(source):
     """Convert a markdown string to ReST via pandoc.
 

setup.py

@@ -274,7 +274,7 b' extras_require = dict('
     terminal = [],
     nbformat = ['jsonschema>=2.0', 'jsonpointer>=1.3'],
     notebook = ['tornado>=3.1', 'pyzmq>=2.1.11', 'jinja2'],
-    nbconvert = ['pygments', 'jinja2', 'Sphinx>=0.3']
+    nbconvert = ['pygments', 'jinja2', 'Sphinx>=0.3', 'mistune']
 )
 
 if sys.version_info < (3, 3):