diff --git a/gflags_validators.py b/gflags_validators.py
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+++ b/gflags_validators.py
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+#!/usr/bin/env python
+
+# Copyright (c) 2010, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+"""Module to enforce different constraints on flags.
+
+A validator represents an invariant, enforced over a one or more flags.
+See 'FLAGS VALIDATORS' in flags.py's docstring for a usage manual.
+"""
+
+__author__ = 'olexiy@google.com (Olexiy Oryeshko)'
+
+
+class Error(Exception):
+  """Thrown If validator constraint is not satisfied."""
+
+
+class Validator(object):
+  """Base class for flags validators.
+
+  Users should NOT overload these classes, and use flags.Register...
+  methods instead.
+  """
+
+  # Used to assign each validator an unique insertion_index
+  validators_count = 0
+
+  def __init__(self, checker, message):
+    """Constructor to create all validators.
+
+    Args:
+      checker: function to verify the constraint.
+        Input of this method varies, see SimpleValidator and
+          DictionaryValidator for a detailed description.
+      message: string, error message to be shown to the user
+    """
+    self.checker = checker
+    self.message = message
+    Validator.validators_count += 1
+    # Used to assert validators in the order they were registered (CL/18694236)
+    self.insertion_index = Validator.validators_count
+
+  def Verify(self, flag_values):
+    """Verify that constraint is satisfied.
+
+    flags library calls this method to verify Validator's constraint.
+    Args:
+      flag_values: flags.FlagValues, containing all flags
+    Raises:
+      Error: if constraint is not satisfied.
+    """
+    param = self._GetInputToCheckerFunction(flag_values)
+    if not self.checker(param):
+      raise Error(self.message)
+
+  def GetFlagsNames(self):
+    """Return the names of the flags checked by this validator.
+
+    Returns:
+      [string], names of the flags
+    """
+    raise NotImplementedError('This method should be overloaded')
+
+  def PrintFlagsWithValues(self, flag_values):
+    raise NotImplementedError('This method should be overloaded')
+
+  def _GetInputToCheckerFunction(self, flag_values):
+    """Given flag values, construct the input to be given to checker.
+
+    Args:
+      flag_values: flags.FlagValues, containing all flags.
+    Returns:
+      Return type depends on the specific validator.
+    """
+    raise NotImplementedError('This method should be overloaded')
+
+
+class SimpleValidator(Validator):
+  """Validator behind RegisterValidator() method.
+
+  Validates that a single flag passes its checker function. The checker function
+  takes the flag value and returns True (if value looks fine) or, if flag value
+  is not valid, either returns False or raises an Exception."""
+  def __init__(self, flag_name, checker, message):
+    """Constructor.
+
+    Args:
+      flag_name: string, name of the flag.
+      checker: function to verify the validator.
+        input  - value of the corresponding flag (string, boolean, etc).
+        output - Boolean. Must return True if validator constraint is satisfied.
+          If constraint is not satisfied, it should either return False or
+          raise Error.
+      message: string, error message to be shown to the user if validator's
+        condition is not satisfied
+    """
+    super(SimpleValidator, self).__init__(checker, message)
+    self.flag_name = flag_name
+
+  def GetFlagsNames(self):
+    return [self.flag_name]
+
+  def PrintFlagsWithValues(self, flag_values):
+    return 'flag --%s=%s' % (self.flag_name, flag_values[self.flag_name].value)
+
+  def _GetInputToCheckerFunction(self, flag_values):
+    """Given flag values, construct the input to be given to checker.
+
+    Args:
+      flag_values: flags.FlagValues
+    Returns:
+      value of the corresponding flag.
+    """
+    return flag_values[self.flag_name].value
+
+
+class DictionaryValidator(Validator):
+  """Validator behind RegisterDictionaryValidator method.
+
+  Validates that flag values pass their common checker function. The checker
+  function takes flag values and returns True (if values look fine) or,
+  if values are not valid, either returns False or raises an Exception.
+  """
+  def __init__(self, flag_names, checker, message):
+    """Constructor.
+
+    Args:
+      flag_names: [string], containing names of the flags used by checker.
+      checker: function to verify the validator.
+        input  - dictionary, with keys() being flag_names, and value for each
+          key being the value of the corresponding flag (string, boolean, etc).
+        output - Boolean. Must return True if validator constraint is satisfied.
+          If constraint is not satisfied, it should either return False or
+          raise Error.
+      message: string, error message to be shown to the user if validator's
+        condition is not satisfied
+    """
+    super(DictionaryValidator, self).__init__(checker, message)
+    self.flag_names = flag_names
+
+  def _GetInputToCheckerFunction(self, flag_values):
+    """Given flag values, construct the input to be given to checker.
+
+    Args:
+      flag_values: flags.FlagValues
+    Returns:
+      dictionary, with keys() being self.lag_names, and value for each key
+        being the value of the corresponding flag (string, boolean, etc).
+    """
+    return dict([key, flag_values[key].value] for key in self.flag_names)
+
+  def PrintFlagsWithValues(self, flag_values):
+    prefix = 'flags '
+    flags_with_values = []
+    for key in self.flag_names:
+      flags_with_values.append('%s=%s' % (key, flag_values[key].value))
+    return prefix + ', '.join(flags_with_values)
+
+  def GetFlagsNames(self):
+    return self.flag_names