Decode input str when reporting an error in parse_isodate

As the function is wrapped around a decorator that converts the input to
bytes, when an exception is raised that includes the value, it contains
the value as bytes (b"<val>"). To provide the expected str in Python 3,
decode that to unicode.

This will result in `u""` for Python 2 callers, but given that we plan
to drop support for Python 2 in the short term, it feels acceptable.

AUTHORS.md

@@ -86,6 +86,7 @@ switch, and thus all their contributions are dual-licensed.
 - Nicolas Évrard (gh: @nicoe) **D**
 - Nick Smith <nick.smith@MASKED>
 - Orson Adams <orson.network@MASKED> (gh: @parsethis) **D**
+- Paul Brown (gh: @pawl) **D**
 - Paul Dickson (gh @prdickson) **D**
 - Paul Ganssle <paul@ganssle.io> (gh: @pganssle) **R**
 - Pascal van Kooten <kootenpv@MASKED> (gh: @kootenpv) **R**

changelog.d/1122.bugfix.rst

@@ -0,0 +1 @@
+Fixed a bug that caused b' prefixes to appear in parse_isodate exception messages.

dateutil/parser/isoparser.py

@@ -159,7 +159,7 @@ def parse_isodate(self, datestr):
         components, pos = self._parse_isodate(datestr)
         if pos < len(datestr):
             raise ValueError('String contains unknown ISO ' +
-                             'components: {}'.format(datestr))
+                             'components: {!r}'.format(datestr.decode('ascii')))
         return date(*components)
 
     @_takes_ascii

dateutil/test/test_isoparser.py

@@ -403,6 +403,18 @@ def test_isodate_raises(isostr, exception):
         isoparser().parse_isodate(isostr)
 
 
+def test_parse_isodate_error_text():
+    with pytest.raises(ValueError) as excinfo:
+        isoparser().parse_isodate('2014-0423')
+
+    # ensure the error message does not contain b' prefixes
+    if six.PY2:
+        expected_error = "String contains unknown ISO components: u'2014-0423'"
+    else:
+        expected_error = "String contains unknown ISO components: '2014-0423'"
+    assert expected_error == str(excinfo.value)
+
+
 ###
 # Test parse_isotime
 def __make_time_examples():