Move definition of ValidationError class next to definition

of validate() function. This change organizes the module so
that functions and classes are defined in the order they
are used in the validate() function itself.

datatest/validation.py

@@ -90,117 +90,6 @@ def _normalize_requirement(requirement):
     return requirement
 
 
-class ValidationError(AssertionError):
-    """This exception is raised when data validation fails."""
-
-    __module__ = 'datatest'
-
-    def __init__(self, differences, description=None):
-        if isinstance(differences, BaseDifference):
-            differences = [differences]
-        elif not nonstringiter(differences):
-            msg = 'expected an iterable of differences, got {0!r}'
-            raise TypeError(msg.format(differences.__class__.__name__))
-
-        # Normalize *differences* argument.
-        if _is_collection_of_items(differences):
-            differences = dict(differences)
-        elif exhaustible(differences):
-            differences = list(differences)
-
-        if not differences:
-            raise ValueError('differences container must not be empty')
-
-        # Initialize properties.
-        self._differences = differences
-        self._description = description
-        self._should_truncate = None
-        self._truncation_notice = None
-
-    @property
-    def differences(self):
-        """A collection of "difference" objects to describe elements
-        in the data under test that do not satisfy the requirement.
-        """
-        return self._differences
-
-    @property
-    def description(self):
-        """An optional description of the failed requirement."""
-        return self._description
-
-    @property
-    def args(self):
-        """The tuple of arguments given to the exception constructor."""
-        return (self._differences, self._description)
-
-    def __str__(self):
-        # Prepare a format-differences callable.
-        if isinstance(self._differences, dict):
-            begin, end = '{', '}'
-            all_keys = sorted(self._differences.keys(), key=_safesort_key)
-            def sorted_value(key):
-                value = self._differences[key]
-                if nonstringiter(value):
-                    sort_args = lambda diff: _safesort_key(diff.args)
-                    return sorted(value, key=sort_args)
-                return value
-            iterator = iter((key, sorted_value(key)) for key in all_keys)
-            format_diff = lambda x: '    {0!r}: {1!r},'.format(x[0], x[1])
-        else:
-            begin, end = '[', ']'
-            sort_args = lambda diff: _safesort_key(diff.args)
-            iterator = iter(sorted(self._differences, key=sort_args))
-            format_diff = lambda x: '    {0!r},'.format(x)
-
-        # Format differences as a list of strings and get line count.
-        if self._should_truncate:
-            line_count = 0
-            char_count = 0
-            list_of_strings = []
-            for x in iterator:                  # For-loop used to build list
-                line_count += 1                 # iteratively to optimize for
-                diff_string = format_diff(x)    # memory (in case the iter of
-                char_count += len(diff_string)  # diffs is extremely long).
-                if self._should_truncate(line_count, char_count):
-                    line_count += sum(1 for x in iterator)
-                    end = '    ...'
-                    if self._truncation_notice:
-                        end += '\n\n{0}'.format(self._truncation_notice)
-                    break
-                list_of_strings.append(diff_string)
-        else:
-            list_of_strings = [format_diff(x) for x in iterator]
-            line_count = len(list_of_strings)
-
-        # Prepare count-of-differences string.
-        count_message = '{0} difference{1}'.format(
-            line_count,
-            '' if line_count == 1 else 's',
-        )
-
-        # Prepare description string.
-        if self._description:
-            description = '{0} ({1})'.format(self._description, count_message)
-        else:
-            description = count_message
-
-        # Prepare final output.
-        output = '{0}: {1}\n{2}\n{3}'.format(
-            description,
-            begin,
-            '\n'.join(list_of_strings),
-            end,
-        )
-        return output
-
-    def __repr__(self):
-        cls_name = self.__class__.__name__
-        if self.description:
-            return '{0}({1!r}, {2!r})'.format(cls_name, self.differences, self.description)
-        return '{0}({1!r})'.format(cls_name, self.differences)
-
-
 def _get_group_requirement(requirement, show_expected=False):
     """Make sure *requirement* is a group requirement."""
     if getattr(requirement, '_group_requirement', False):
@@ -320,6 +209,117 @@ def _datadict_vs_requirementdict(data, requirement):
     return differences, description
 
 
+class ValidationError(AssertionError):
+    """This exception is raised when data validation fails."""
+
+    __module__ = 'datatest'
+
+    def __init__(self, differences, description=None):
+        if isinstance(differences, BaseDifference):
+            differences = [differences]
+        elif not nonstringiter(differences):
+            msg = 'expected an iterable of differences, got {0!r}'
+            raise TypeError(msg.format(differences.__class__.__name__))
+
+        # Normalize *differences* argument.
+        if _is_collection_of_items(differences):
+            differences = dict(differences)
+        elif exhaustible(differences):
+            differences = list(differences)
+
+        if not differences:
+            raise ValueError('differences container must not be empty')
+
+        # Initialize properties.
+        self._differences = differences
+        self._description = description
+        self._should_truncate = None
+        self._truncation_notice = None
+
+    @property
+    def differences(self):
+        """A collection of "difference" objects to describe elements
+        in the data under test that do not satisfy the requirement.
+        """
+        return self._differences
+
+    @property
+    def description(self):
+        """An optional description of the failed requirement."""
+        return self._description
+
+    @property
+    def args(self):
+        """The tuple of arguments given to the exception constructor."""
+        return (self._differences, self._description)
+
+    def __str__(self):
+        # Prepare a format-differences callable.
+        if isinstance(self._differences, dict):
+            begin, end = '{', '}'
+            all_keys = sorted(self._differences.keys(), key=_safesort_key)
+            def sorted_value(key):
+                value = self._differences[key]
+                if nonstringiter(value):
+                    sort_args = lambda diff: _safesort_key(diff.args)
+                    return sorted(value, key=sort_args)
+                return value
+            iterator = iter((key, sorted_value(key)) for key in all_keys)
+            format_diff = lambda x: '    {0!r}: {1!r},'.format(x[0], x[1])
+        else:
+            begin, end = '[', ']'
+            sort_args = lambda diff: _safesort_key(diff.args)
+            iterator = iter(sorted(self._differences, key=sort_args))
+            format_diff = lambda x: '    {0!r},'.format(x)
+
+        # Format differences as a list of strings and get line count.
+        if self._should_truncate:
+            line_count = 0
+            char_count = 0
+            list_of_strings = []
+            for x in iterator:                  # For-loop used to build list
+                line_count += 1                 # iteratively to optimize for
+                diff_string = format_diff(x)    # memory (in case the iter of
+                char_count += len(diff_string)  # diffs is extremely long).
+                if self._should_truncate(line_count, char_count):
+                    line_count += sum(1 for x in iterator)
+                    end = '    ...'
+                    if self._truncation_notice:
+                        end += '\n\n{0}'.format(self._truncation_notice)
+                    break
+                list_of_strings.append(diff_string)
+        else:
+            list_of_strings = [format_diff(x) for x in iterator]
+            line_count = len(list_of_strings)
+
+        # Prepare count-of-differences string.
+        count_message = '{0} difference{1}'.format(
+            line_count,
+            '' if line_count == 1 else 's',
+        )
+
+        # Prepare description string.
+        if self._description:
+            description = '{0} ({1})'.format(self._description, count_message)
+        else:
+            description = count_message
+
+        # Prepare final output.
+        output = '{0}: {1}\n{2}\n{3}'.format(
+            description,
+            begin,
+            '\n'.join(list_of_strings),
+            end,
+        )
+        return output
+
+    def __repr__(self):
+        cls_name = self.__class__.__name__
+        if self.description:
+            return '{0}({1!r}, {2!r})'.format(cls_name, self.differences, self.description)
+        return '{0}({1!r})'.format(cls_name, self.differences)
+
+
 def validate(data, requirement, msg=None):
     """Raise a :exc:`ValidationError` if *data* does not satisfy
     *requirement* or pass without error if data is valid.