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diff --git a/resources/libraries/python/MLRsearch/expander.py b/resources/libraries/python/MLRsearch/expander.py
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+# Copyright (c) 2023 Cisco and/or its affiliates.
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at:
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Module defining TargetExpander class."""
+
+
+from dataclasses import dataclass, field
+from typing import Callable, Optional
+
+from .dataclass import secondary_field
+from .discrete_load import DiscreteLoad
+from .discrete_width import DiscreteWidth
+from .global_width import GlobalWidth
+from .limit_handler import LimitHandler
+from .target_spec import TargetSpec
+
+
+@dataclass
+class TargetedExpander:
+    """Utility class to track expanding width during external search.
+
+    One instance per selector but takes into consideration global current width.
+
+    Generally, many strategies may limit next_width immediately,
+    but next_width expands only after measurement
+    when external search fails to find its bound (global width is also bumped).
+    See strategy classes for specific details on external and internal search.
+    """
+
+    target: TargetSpec
+    """The target this strategy is focusing on."""
+    global_width: GlobalWidth
+    """Reference to the global width tracking instance."""
+    initial_lower_load: Optional[DiscreteLoad]
+    """Smaller of the two loads distinguished at instance creation.
+    Can be None if initial upper bound is the min load."""
+    initial_upper_load: Optional[DiscreteLoad]
+    """Larger of the two loads distinguished at instance creation.
+    Can be None if initial lower bound is the max load."""
+    handler: LimitHandler = field(repr=False)
+    """Reference to the class used to avoid too narrow intervals."""
+    debug: Callable[[str], None] = field(repr=False)
+    """Injectable function for debug logging."""
+    # Primary above, derived below.
+    next_width: DiscreteWidth = secondary_field()
+    """This will be used in next search step if no strategy intervenes."""
+
+    def __post_init__(self) -> None:
+        """Prepare next width."""
+        self.next_width = self.target.discrete_width
+        if self.initial_lower_load and self.initial_upper_load:
+            interval_width = self.initial_upper_load - self.initial_lower_load
+            self.next_width = max(self.next_width, interval_width)
+        self.expand(bump_global=False)
+
+    def expand(self, bump_global: bool = True) -> None:
+        """Multiply next width by expansion coefficient.
+
+        The global current width should be bumped when external search
+        is done but load is not the bound we were looking for.
+
+        For global width shrinking, set the field directly.
+
+        :param bump_global: False if called from limit or post init.
+        :type bump_global: bool
+        """
+        self.next_width *= self.target.expansion_coefficient
+        if bump_global:
+            self.global_width.width = self.next_width
+
+    def get_width(self) -> DiscreteWidth:
+        """Return next width corrected by global current width.
+
+        :returns: The width to use, see GlobalWidth.
+        :rtype: DiscreteWidth
+        """
+        return self.global_width.or_larger(self.next_width)
+
+    def limit(self, last_width: DiscreteWidth) -> None:
+        """Decrease the prepared next width.
+
+        This is called by other strategies when bounds are getting narrower.
+
+        Global current width is not updated yet,
+        as the other strategy may not end up becoming the winner
+        and we want to avoid interfering with other selector strategies.
+
+        :param last_width: As applied by other strategy, smaller of two halves.
+        :type last_width: DiscreteWidth
+        """
+        self.next_width = max(last_width, self.target.discrete_width)
+        self.expand(bump_global=False)