pandoc version is now checked at each call to pandoc.pandoc(...). Version is tested with IPython.utils.version.version_check

IPython/nbconvert/utils/pandoc.py

@@ -21,6 +21,8 b' from io import TextIOWrapper, BytesIO'
 
 # IPython imports
 from IPython.utils.py3compat import cast_bytes
+from IPython.utils.version import check_version
+
 
 from .exceptions import ConversionException
 
@@ -85,11 +87,12 b' def pandoc_available(failmode="return", warn=False, alt=None):'
 
 
 minimal_version = "1.12.1"
+minimal_version_ok = False
 
 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.
+    This function will raise PandocMissing if pandoc is not installed.
     Any error messages generated by pandoc are printed to stderr.
 
     Parameters
@@ -112,6 +115,7 b" def pandoc(source, fmt, to, extra_args=None, encoding='utf-8'):"
 
     # if pandoc is missing let the exception bubble us out of here
     pandoc_available(failmode="raise", alt=cmd)
+    check_pandoc_version()
     
     # we can safely continue
     p = subprocess.Popen(cmd, stdin=subprocess.PIPE, stdout=subprocess.PIPE)
@@ -121,22 +125,34 b" def pandoc(source, fmt, to, extra_args=None, encoding='utf-8'):"
 
 
 def get_pandoc_version():
-    """Gets the Pandoc version if Pandoc is installed."""
+    """Gets the Pandoc version if Pandoc is installed.
+    PandocMissing will be raised if pandoc is unavailable.
+    """
     try:
+        if not minimal_version_ok:
+            raise AttributeError()
+        else:
         return pandoc.version
     except AttributeError:
-        out = pandoc("None", "None", "None", ["-v"])
+        cmd = ["pandoc", "-v"]
+        try:
+            out = subprocess.check_output(cmd, universal_newlines=True)
+        except OSError as e:
+            raise PandocMissing(cmd, e)
         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()):
+    """Returns True if minimal pandoc version is met.
+    PandocMissing will be raised if pandoc is unavailable.
+    """
+    global minimal_version_ok
+    if not minimal_version_ok:
+        minimal_version_ok = check_version( get_pandoc_version(), minimal_version )
+        if not minimal_version_ok:
         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)
+    return minimal_version_ok