command.extend in pandoc

IPython/nbconvert/utils/pandoc.py

@@ -1,56 +1,56 b''
 """Utility for calling pandoc"""
 #-----------------------------------------------------------------------------
 # 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 __future__ import print_function
 
 # Stdlib imports
 import sys
 import subprocess
 
 # IPython imports
 from IPython.utils.py3compat import cast_bytes
 
 #-----------------------------------------------------------------------------
 # Classes and functions
 #-----------------------------------------------------------------------------
 
 def pandoc(source, fmt, to, extra_args=None, encoding='utf-8'):
     """Convert an input string in format `from` to format `to` via pandoc.
 
     This function will raise an error if pandoc is not installed.
     Any error messages generated by pandoc are printed to stderr.
 
     Parameters
     ----------
     source : string
       Input string, assumed to be valid format `from`.
     fmt : string
       The name of the input format (markdown, etc.)
     to : string
       The name of the output format (html, etc.)
 
     Returns
     -------
     out : unicode
       Output as returned by pandoc.
     """
     command = ['pandoc', '-f', fmt, '-t', to]
     if extra_args:
-        command = command + extra_args
+        command.extend(extra_args)
     p = subprocess.Popen(command,
                          stdin=subprocess.PIPE, stdout=subprocess.PIPE
     )
     out, _ = p.communicate(cast_bytes(source, encoding))
     out = out.decode(encoding, 'replace')
     return out[:-1]