Reformat IOErrors in converter.file

clize/errors.py

@@ -111,17 +111,21 @@ def message(self):
                 self.param)
 
 
+class CliValueError(ValueError):
+    """Specialization of `ValueError` for showing a message to the user along
+    with the error rather than just the incorrect value."""
+
 class BadArgumentFormat(ArgumentError):
     """Raised when an argument cannot be converted to the correct format."""
 
-    def __init__(self, param, val):
+    def __init__(self, param, text):
         self.param = param
-        self.val = val
+        self.text = text
 
     @property
     def message(self):
-        return "Bad value for {0.display_name}: {1!r}".format(
-            self.param, self.val)
+        return "Bad value for {0.display_name}: {1}".format(
+            self.param, self.text)
 
 
 class ArgsBeforeAlternateCommand(ArgumentError):

clize/extra/converters.py

@@ -6,13 +6,23 @@
 
 from dateutil import parser as dparser
 
+from clize import errors
+
 
 def datetime(arg):
     return dparser.parse(arg)
 
 
 def file(**kwargs):
     def file_(arg):
-        return io.open(arg, **kwargs)
+        try:
+            return io.open(arg, **kwargs)
+        except IOError as exc:
+            raise _convert_ioerror(arg, exc)
+
     return file_
 
+def _convert_ioerror(arg, exc):
+    nexc = errors.CliValueError('{0.strerror} {1!r}'.format(exc, arg))
+    nexc.__cause__ = exc
+    return nexc

clize/parser.py

@@ -201,16 +201,21 @@ def coerce_value(self, arg, ba):
         """
         try:
             ret = self.typ(arg)
+        except errors.CliValueError as e:
+            exc = errors.BadArgumentFormat(self, e)
+            exc.__cause__ = e
+            raise exc
+        except ValueError as e:
+            exc = errors.BadArgumentFormat(self, repr(arg))
+            exc.__cause__ = e
+            raise exc
+        else:
             try:
                 type(ret).__enter__
             except AttributeError:
                 return ret
             else:
                 return ba.exitstack.enter_context(ret)
-        except ValueError as e:
-            exc = errors.BadArgumentFormat(self.typ, arg)
-            exc.__cause__ = e
-            raise exc
 
     def get_value(self, ba, i):
         """Retrieves the "value" part of the argument in ``ba`` at

clize/tests/extra/test_converters.py

@@ -66,6 +66,11 @@ def test_file_write(self):
         self.assertEqual(arg.mode, 'w')
         self.assertTrue(arg.closed)
 
+    def test_file_missing(self):
+        path = os.path.join(self.temp, 'afile')
+        self.assertRaises(errors.BadArgumentFormat,
+                          self.run_conv, converters.file(), path)
+
 
 @util.repeated_test
 class ConverterErrorTests(object):