IPython/nbconvert/utils/pandoc.py

"""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, 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 as e:
        if warn:
            warnings.warn(
                "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(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", 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)