python-jsonschema#708 - conditional message code for old Python

For Python interpreters that don't treat multibyte Unicode characters as single characters, add some code to manually calculate the number of bar characters required to reach the desired line length.  This code is confined to a conditional block and may be removed when support for older interpreters is no longer needed.

Author: sloanlance

jsonschema/cli.py

@@ -15,7 +15,7 @@
 
 from jsonschema import __version__
 from jsonschema._reflect import namedAny
-from jsonschema.compat import PY3, JSONDecodeError
+from jsonschema.compat import JSONDecodeError
 from jsonschema.exceptions import SchemaError
 from jsonschema.validators import validator_for
 
@@ -70,35 +70,44 @@ def validation_success(self, **kwargs):
 
 @attr.s
 class _PrettyFormatter(object):
-
-    _WIDTH = 79
-    _HEADER_LINE = '═'
+    _MESSAGE_BAR_CHAR = '═'
+    _MESSAGE_CORNER_CHARS = ('╒', '╕')
     _MESSAGE_FORMAT = '{}══[{}]═══({})'
+    _MESSAGE_MAX_LENGTH = 79
 
     @classmethod
     def _json_formatter(cls, x):
         return json.dumps(x, separators=(',\n', ': '), sort_keys=True)
 
-    def _simple_msg_v3(self, path, type, header=False):
-        begin_end_chars = ('╒', '╕') if header is True else ('═', '═')
-        return '{}══[{}]═══({})'.format(begin_end_chars[0], type, path) \
-                   .ljust(self._WIDTH - 1, '═') + begin_end_chars[1]
+    def _message_end_chars(self, header=False):
+        return self._MESSAGE_CORNER_CHARS if header is True else [self._MESSAGE_BAR_CHAR] * 2
+
+    def _message_line(self, path, type, header=False):
+        begin_char, end_char = self._message_end_chars(header)
+        return self._MESSAGE_FORMAT.format(begin_char, type, path) \
+            .ljust(self._MESSAGE_MAX_LENGTH - 1, self._MESSAGE_BAR_CHAR) + end_char
+
+    if len(_MESSAGE_BAR_CHAR) != 1:
+        # The code in this if-block is for Python interpreters that don't
+        # treat multibyte Unicode characters as single characters.
+        # E.g., some versions of Python 2.x.  This block may be removed
+        # when support for those interpreters is no longer needed.
+
+        _FORMAT_LENGTH = len(
+            _MESSAGE_FORMAT.replace(_MESSAGE_BAR_CHAR, '.').format('.', '', '')) + 1
 
-    def _simple_msg_v2(self, path, type, header=False):
-        begin_end_chars = ('╒', '╕') if header is True else ('═', '═')
+        def _message_line(self, path, type, header=False):
+            begin_char, end_char = self._message_end_chars(header)
 
-        # printed length of the static charaters: left end, brackets, bar characters
-        format_length = 11  # TODO: calculate fixed chars printed length
-        desired_length = self._WIDTH - len(type) - len(path) - format_length
+            bar_length = self._MESSAGE_MAX_LENGTH - len(type) - len(path) - self._FORMAT_LENGTH
 
-        return self._MESSAGE_FORMAT.format(begin_end_chars[0], type, path) + \
-               self._HEADER_LINE * desired_length + begin_end_chars[1]
+            return self._MESSAGE_FORMAT.format(begin_char, type, path) + \
+                self._MESSAGE_BAR_CHAR * bar_length + end_char
 
-    _simple_msg = _simple_msg_v3 if len(_HEADER_LINE) == 1 else _simple_msg_v2
 
     def _error_msg(self, path, type, body):
-        HEADER = self._simple_msg(path, type, header=True)
-        FOOTER = '└' + '─' * (self._WIDTH - 2) + '┘'
+        HEADER = self._message_line(path, type, header=True)
+        FOOTER = '└' + '─' * (self._MESSAGE_MAX_LENGTH - 2) + '┘'
 
         return '\n'.join((HEADER, str(body), FOOTER, '\n'))
 
@@ -128,7 +137,7 @@ def validation_error(self, instance_path, error):
         )
 
     def validation_success(self, instance_path):
-        return self._simple_msg(path=instance_path, type='SUCCESS') + '\n\n'
+        return self._message_line(path=instance_path, type='SUCCESS') + '\n\n'
 
 
 @attr.s