never import pigments at module level in nbconvert

ensures things are always importable, and delays ImportErrors until they are actually relevant.

IPython/nbconvert/filters/highlight.py

@@ -1,121 +1,123 b''
 """
 Module containing filter functions that allow code to be highlighted
 from within Jinja templates.
 """
 #-----------------------------------------------------------------------------
 # Copyright (c) 2013, the IPython Development Team.
 #
 # Distributed under the terms of the Modified BSD License.
 #
 # The full license is in the file COPYING.txt, distributed with this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 
-from pygments import highlight as pygements_highlight
-from pygments.lexers import get_lexer_by_name
-from pygments.formatters import HtmlFormatter
-from pygments.formatters import LatexFormatter
-
+# pygments must not be imported at the module level
+# because errors should be raised at runtime if it's actually needed,
+# not import time, when it may not be needed.
 
 # Our own imports
-from IPython.nbconvert.utils.lexers import IPythonLexer
 from IPython.nbconvert.utils.base import NbConvertBase
 
 #-----------------------------------------------------------------------------
 # Globals and constants
 #-----------------------------------------------------------------------------
 
 MULTILINE_OUTPUTS = ['text', 'html', 'svg', 'latex', 'javascript', 'json']
 
 #-----------------------------------------------------------------------------
 # Utility functions
 #-----------------------------------------------------------------------------
 
 __all__ = [
     'Highlight2Html',
     'Highlight2Latex'
 ]
 
 
 class Highlight2Html(NbConvertBase):
 
     def __call__(self, source, language=None, metadata=None):
         """
         Return a syntax-highlighted version of the input source as html output.
 
         Parameters
         ----------
         source : str
             source of the cell to highlight
         language : str
             language to highlight the syntax of
         metadata : NotebookNode cell metadata
             metadata of the cell to highlight
         """
+        from pygments.formatters import HtmlFormatter
         if not language:
             language=self.default_language
 
-        return _pygment_highlight(source, HtmlFormatter(), language, metadata)
+        return _pygments_highlight(source, HtmlFormatter(), language, metadata)
 
 
 class Highlight2Latex(NbConvertBase):
 
     def __call__(self, source, language=None, metadata=None, strip_verbatim=False):
         """
         Return a syntax-highlighted version of the input source as latex output.
 
         Parameters
         ----------
         source : str
             source of the cell to highlight
         language : str
             language to highlight the syntax of
         metadata : NotebookNode cell metadata
             metadata of the cell to highlight
         strip_verbatim : bool
             remove the Verbatim environment that pygments provides by default
         """
+        from pygments.formatters import LatexFormatter
         if not language:
             language=self.default_language
 
-        latex = _pygment_highlight(source, LatexFormatter(), language, metadata)
+        latex = _pygments_highlight(source, LatexFormatter(), language, metadata)
         if strip_verbatim:
             latex = latex.replace(r'\begin{Verbatim}[commandchars=\\\{\}]' + '\n', '')
             return latex.replace('\n\\end{Verbatim}\n', '')
         else:
             return latex
 
 
 
-def _pygment_highlight(source, output_formatter, language='ipython', metadata=None):
+def _pygments_highlight(source, output_formatter, language='ipython', metadata=None):
     """
     Return a syntax-highlighted version of the input source
 
     Parameters
     ----------
     source : str
         source of the cell to highlight
     output_formatter : Pygments formatter
     language : str
         language to highlight the syntax of
     metadata : NotebookNode cell metadata
         metadata of the cell to highlight
     """
+    from pygments import highlight
+    from pygments.lexers import get_lexer_by_name
+    from IPython.nbconvert.utils.lexers import IPythonLexer
 
     # If the cell uses a magic extension language,
     # use the magic language instead.
     if language == 'ipython' \
         and metadata \
         and 'magics_language' in metadata:
 
         language = metadata['magics_language']
 
     if language == 'ipython':
         lexer = IPythonLexer()
     else:
         lexer = get_lexer_by_name(language, stripall=True)
 
-    return pygements_highlight(source, lexer, output_formatter)
+    return highlight(source, lexer, output_formatter)

IPython/nbconvert/preprocessors/csshtmlheader.py

@@ -1,106 +1,105 b''
 """Module that pre-processes the notebook for export to HTML.
 """
 #-----------------------------------------------------------------------------
 # Copyright (c) 2013, the IPython Development Team.
 #
 # Distributed under the terms of the Modified BSD License.
 #
 # The full license is in the file COPYING.txt, distributed with this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 
 import os
 import io
 
-from pygments.formatters import HtmlFormatter
-
 from IPython.utils import path
 
 from .base import Preprocessor
 
 from IPython.utils.traitlets import Unicode
 
 #-----------------------------------------------------------------------------
 # Classes and functions
 #-----------------------------------------------------------------------------
 
 class CSSHTMLHeaderPreprocessor(Preprocessor):
     """
     Preprocessor used to pre-process notebook for HTML output.  Adds IPython notebook
     front-end CSS and Pygments CSS to HTML output.
     """
 
     header = []
 
     highlight_class = Unicode('.highlight', config=True,
                               help="CSS highlight class identifier")
 
     def __init__(self, config=None, **kw):
         """
         Public constructor
         
         Parameters
         ----------
         config : Config
             Configuration file structure
         **kw : misc
             Additional arguments
         """
         
         super(CSSHTMLHeaderPreprocessor, self).__init__(config=config, **kw)
 
         if self.enabled :
             self._regen_header()
 
 
     def preprocess(self, nb, resources):
         """Fetch and add CSS to the resource dictionary
 
         Fetch CSS from IPython and Pygments to add at the beginning
         of the html files.  Add this css in resources in the 
         "inlining.css" key
         
         Parameters
         ----------
         nb : NotebookNode
             Notebook being converted
         resources : dictionary
             Additional resources used in the conversion process.  Allows
             preprocessors to pass variables into the Jinja engine.
         """
         
         resources['inlining'] = {}
         resources['inlining']['css'] = self.header
         
         return nb, resources
 
 
     def _regen_header(self):
         """ 
         Fills self.header with lines of CSS extracted from IPython 
         and Pygments.
         """
+        from pygments.formatters import HtmlFormatter
         
         #Clear existing header.
         header = []
         
         #Construct path to IPy CSS
         sheet_filename = os.path.join(path.get_ipython_package_dir(), 
             'html', 'static', 'style', 'style.min.css')
         
         #Load style CSS file.
         with io.open(sheet_filename, encoding='utf-8') as file:
             file_text = file.read()
             header.append(file_text)
 
         #Add pygments CSS
         formatter = HtmlFormatter()
         pygments_css = formatter.get_style_defs(self.highlight_class)
         header.append(pygments_css)
 
         #Set header        
         self.header = header