Fix exception handler syntax for Python 3 compatibility.

Improve error messages.

IPython/nbconvert/utils/pandoc.py

@@ -1,140 +1,142 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 subprocess
 import re
 import warnings
 from io import TextIOWrapper, BytesIO
 
 # IPython imports
 from IPython.utils.py3compat import cast_bytes
 
 from .exceptions import ConversionException
 
 
 #----------------------------------------------------------------------------
 # Preliminary checks.
 # Not finding Pandoc is not always fatal so only a warning is issued at the
 # module root level so that the import of this module is not fatal. 
 #----------------------------------------------------------------------------
 
 class PandocMissing(ConversionException):
     """Exception raised when Pandoc is missing. """
     def __init__(self, cmd, exc, *args, **kwargs):
         super(PandocMissing, self).__init__( "The command '%s' returned an error: %s.\n" %(" ".join(cmd), exc) +
                                              "Please check that pandoc is installed:\n" +
                                              "http://johnmacfarlane.net/pandoc/installing.html" )
 
-def pandoc_available(failmode="return", warn=False):
+def pandoc_available(failmode="return", warn=False, alt=None):
     """Is pandoc available. Only tries to call Pandoc
     and inform you that it succeeded or failed. 
     
     Parameters
     ----------
      - failmode : string
         either "return" or "raise". If "return" and pandoc
         is not available, will return (False, e) where e is
         the exception returned by subprocess.check_call.
      - warn : bool
         issue a user warning if pandoc is not available.
+     - alt: list of strings
+        command to print in the error (not used as actual call)
 
     Return
     ------
     out : (Bool, Exception)
         On success will return (True, None). On failure and failmode=="return" 
         will return (False, OSError instance)
     """
     
     cmd  = ["pandoc", "-v"]
 
     try:
         out = subprocess.check_output(cmd, universal_newlines=True)
         return True, None
-    except OSError, e:
+    except OSError as e:
         if warn:
             warnings.warn(
-                "Pandoc cannot be found (call %s failed).\n" % " ".join(cmd) +
+                "Pandoc cannot be found (calling %s failed).\n" % " ".join(alt or cmd) +
                 "Please check that pandoc is installed:\n" +
                 "http://johnmacfarlane.net/pandoc/installing.html"
             )
 
         if failmode == "return":
             return False, e
         else:
-            raise PandocMissing(cmd, e)
+            raise PandocMissing(alt or cmd, e)
             
 
 #-----------------------------------------------------------------------------
 # Classes and functions
 #-----------------------------------------------------------------------------
 
 
 minimal_version = "1.12.1"
 
 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.
     """
     cmd = ['pandoc', '-f', fmt, '-t', to]
     if extra_args:
         cmd.extend(extra_args)
 
     # if pandoc is missing let the exception bubble us out of here
-    pandoc_available(failmode="raise")
+    pandoc_available(failmode="raise", alt=cmd)
     
     # we can safely continue
     p = subprocess.Popen(cmd, stdin=subprocess.PIPE, stdout=subprocess.PIPE)
     out, _ = p.communicate(cast_bytes(source, encoding))
     out = TextIOWrapper(BytesIO(out), encoding, 'replace').read()
     return out.rstrip('\n')
 
 
 def get_pandoc_version():
     """Gets the Pandoc version if Pandoc is installed."""
     try:
         return pandoc.version
     except AttributeError:
         out = pandoc("None", "None", "None", ["-v"])
         pv_re = re.compile(r'(\d{0,3}\.\d{0,3}\.\d{0,3})')
         pandoc.version = pv_re.search(out).group(0)
         return pandoc.version
 
 def check_pandoc_version():
     """Returns True if minimal pandoc version is met"""
     return get_pandoc_version() >= minimal_version
 
 if pandoc_available(warn=True)[0]:
     if(not check_pandoc_version()):
         warnings.warn( "You are using an old version of pandoc (%s)\n" % pandoc.version + 
                        "Recommended version is %s.\nTry updating." % minimal_version + 
                        "http://johnmacfarlane.net/pandoc/installing.html.\nContinuing with doubts...",
                        RuntimeWarning, stacklevel=2)