Allow defining multi fields with any Iterable, not just lists.

This was motivated to allow tuples as input, but was expanded to allow any
iterable. Strings and non-iterables are still special cased and converted
to a single-element list. A copy of the input iterable is made so that
the flag has sole ownership over the set of values.

NOTE: Custom MultiFlag behavior change: The items of the iterable, rather than
the iterable itself, are now passed onto the underlying self.parser object.
Custom flags using DEFINE_multi or MultiFlag should update their custom flag
code as appropriate.

NOTE: Heavily modified from original PR to adjust for various lint/style
errors and from the auto-formatter.

Resolves #78
Closes #80

PiperOrigin-RevId: 226230348

4 files changed, 48 insertions, 9 deletions

diff --git a/absl/flags/BUILD b/absl/flags/BUILD
index 111cf64..f23bb76 100644
--- a/absl/flags/BUILD
+++ b/absl/flags/BUILD
@@ -68,6 +68,7 @@ py_library(
         ":_argument_parser",
         ":_exceptions",
         ":_helpers",
+        "@six_archive//:six",
     ],
 )
 
diff --git a/absl/flags/_defines.py b/absl/flags/_defines.py
index 73ce8c7..b95c419 100644
--- a/absl/flags/_defines.py
+++ b/absl/flags/_defines.py
@@ -420,7 +420,11 @@ def DEFINE_multi(  # pylint: disable=invalid-name,redefined-builtin
     parser: ArgumentParser, used to parse the flag arguments.
     serializer: ArgumentSerializer, the flag serializer instance.
     name: str, the flag name.
-    default: list|str|None, the default value of the flag.
+    default: Union[Iterable[T], Text, None], the default value of the flag.
+        If the value is text, it will be parsed as if it was provided from
+        the command line. If the value is a non-string iterable, it will be
+        iterated over to create a shallow copy of the values. If it is None,
+        it is left as-is.
     help: str, the help message.
     flag_values: FlagValues, the FlagValues instance with which the flag will
         be registered. This should almost never need to be overridden.
@@ -445,7 +449,8 @@ def DEFINE_multi_string(  # pylint: disable=invalid-name,redefined-builtin
 
   Args:
     name: str, the flag name.
-    default: [str]|str|None, the default value of the flag.
+    default: Union[Iterable[Text], Text, None], the default value of the flag;
+        see `DEFINE_multi`.
     help: str, the help message.
     flag_values: FlagValues, the FlagValues instance with which the flag will
         be registered. This should almost never need to be overridden.
@@ -469,7 +474,8 @@ def DEFINE_multi_integer(  # pylint: disable=invalid-name,redefined-builtin
 
   Args:
     name: str, the flag name.
-    default: [int]|str|None, the default value of the flag.
+    default: Union[Iterable[int], Text, None], the default value of the flag;
+        see `DEFINE_multi`.
     help: str, the help message.
     lower_bound: int, min values of the flag.
     upper_bound: int, max values of the flag.
@@ -495,7 +501,8 @@ def DEFINE_multi_float(  # pylint: disable=invalid-name,redefined-builtin
 
   Args:
     name: str, the flag name.
-    default: [float]|str|None, the default value of the flag.
+    default: Union[Iterable[float], Text, None], the default value of the flag;
+        see `DEFINE_multi`.
     help: str, the help message.
     lower_bound: float, min values of the flag.
     upper_bound: float, max values of the flag.
@@ -521,7 +528,8 @@ def DEFINE_multi_enum(  # pylint: disable=invalid-name,redefined-builtin
 
   Args:
     name: str, the flag name.
-    default: [str]|str|None, the default value of the flag.
+    default: Union[Iterable[Text], Text, None], the default value of the flag;
+        see `DEFINE_multi`.
     enum_values: [str], a non-empty list of strings with the possible values for
         the flag.
     help: str, the help message.
@@ -551,8 +559,12 @@ def DEFINE_multi_enum_class(  # pylint: disable=invalid-name,redefined-builtin
 
   Args:
     name: str, the flag name.
-    default: [Enum]|Enum|[str]|str|None, the default value of the flag. A string
-        or a list of strings will be converted to the equivalent Enum objects.
+    default: Union[Iterable[Enum], Iterable[Text], Enum, Text, None], the
+        default value of the flag; see
+        `DEFINE_multi`; only differences are documented here. If the value is
+        a single Enum, it is treated as a single-item list of that Enum value.
+        If it is an iterable, text values within the iterable will be converted
+        to the equivalent Enum objects.
     enum_class: class, the Enum class with all the possible values for the flag.
         help: str, the help message.
     flag_values: FlagValues, the FlagValues instance with which the flag will be
diff --git a/absl/flags/_flag.py b/absl/flags/_flag.py
index 7568ed7..8e720ec 100644
--- a/absl/flags/_flag.py
+++ b/absl/flags/_flag.py
@@ -22,12 +22,14 @@ from __future__ import absolute_import
 from __future__ import division
 from __future__ import print_function
 
+import collections
 import copy
 import functools
 
 from absl.flags import _argument_parser
 from absl.flags import _exceptions
 from absl.flags import _helpers
+import six
 
 
 @functools.total_ordering
@@ -358,8 +360,8 @@ class MultiFlag(Flag):
   See the __doc__ for Flag for most behavior of this class.  Only
   differences in behavior are described here:
 
-    * The default value may be either a single value or a list of values.
-      A single value is interpreted as the [value] singleton list.
+    * The default value may be either a single value or an iterable of values.
+      A single value is transformed into a single-item list of that value.
 
     * The value of the flag is always a list, even if the option was
       only supplied once, and even if the default value is a single
@@ -386,6 +388,10 @@ class MultiFlag(Flag):
     self.present += len(new_values)
 
   def _parse(self, arguments):
+    if (isinstance(arguments, collections.Iterable) and
+        not isinstance(arguments, six.string_types)):
+      arguments = list(arguments)
+
     if not isinstance(arguments, list):
       # Default value may be a list of values.  Most other arguments
       # will not be, so convert them into a single-item list to make
diff --git a/absl/flags/tests/flags_test.py b/absl/flags/tests/flags_test.py
index 90094d3..ac77707 100644
--- a/absl/flags/tests/flags_test.py
+++ b/absl/flags/tests/flags_test.py
@@ -1184,6 +1184,26 @@ class MultiNumericalFlagsTest(absltest.TestCase):
         expected_floats, FLAGS.get_flag_value('m_float', None)):
       self.assertAlmostEqual(expected, actual)
 
+  def test_multi_numerical_with_tuples(self):
+    """Verify multi_int/float accept tuples as default values."""
+    flags.DEFINE_multi_integer(
+        'm_int_tuple',
+        (77, 88),
+        'integer option that can occur multiple times',
+        short_name='mi_tuple')
+    self.assertListEqual(FLAGS.get_flag_value('m_int_tuple', None), [77, 88])
+
+    dict_with_float_keys = {2.2: 'hello', 3: 'happy'}
+    float_defaults = dict_with_float_keys.keys()
+    flags.DEFINE_multi_float(
+        'm_float_tuple',
+        float_defaults,
+        'float option that can occur multiple times',
+        short_name='mf_tuple')
+    for (expected, actual) in zip(float_defaults,
+                                  FLAGS.get_flag_value('m_float_tuple', None)):
+      self.assertAlmostEqual(expected, actual)
+
   def test_single_value_default(self):
     """Test multi_int and multi_float flags with a single default value."""
     int_default = 77