Randomization Assignment Function (#2)

* add config param

* add assignment test

* fix linter errors

* fix linter error

* use pydantic for models

* rename flag -> experiment_key

Author: ploomiz

.gitignore

@@ -4,3 +4,4 @@ dist/
 .env
 __pycache__
 .tox/
+test-data

LICENSE

@@ -1,201 +1,21 @@
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+MIT License
+
+Copyright (c) 2022 Eppo Data, Inc.
+
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+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

eppo_client/base_model.py

@@ -0,0 +1,14 @@
+from pydantic import BaseModel
+
+
+def to_camel(s: str):
+    words = s.split("_")
+    if len(words) > 1:
+        return words[0] + "".join([w.capitalize() for w in words[1:]])
+    return words[0]
+
+
+class SdkBaseModel(BaseModel):
+    class Config:
+        alias_generator = to_camel
+        allow_population_by_field_name = True

eppo_client/client.py

@@ -0,0 +1,58 @@
+from typing import Optional
+from eppo_client.configuration_requestor import (
+    ExperimentConfigurationDto,
+    ExperimentConfigurationRequestor,
+)
+from eppo_client.shard import get_shard, is_in_shard_range
+from eppo_client.validation import validate_not_blank
+
+
+class EppoClient:
+    def __init__(self, config_requestor: ExperimentConfigurationRequestor) -> None:
+        self.__config_requestor = config_requestor
+
+    def assign(self, subject: str, experiment_key: str) -> Optional[str]:
+        """Maps a subject to a variation for a given experiment
+        Returns None if the subject is not part of the experiment sample.
+
+        :param subject: an entity ID, e.g. userId
+        :param experiment_key: an experiment identifier
+        """
+        validate_not_blank("subject", subject)
+        validate_not_blank("experiment_key", experiment_key)
+        experiment_config = self.__config_requestor.get_configuration(experiment_key)
+        if (
+            experiment_config is None
+            or not experiment_config.enabled
+            or not self.is_in_experiment_sample(
+                subject, experiment_key, experiment_config
+            )
+        ):
+            return None
+        shard = get_shard(
+            "assignment-{}-{}".format(subject, experiment_key),
+            experiment_config.subject_shards,
+        )
+        return next(
+            (
+                variation.name
+                for variation in experiment_config.variations
+                if is_in_shard_range(shard, variation.shard_range)
+            ),
+            None,
+        )
+
+    def is_in_experiment_sample(
+        self,
+        subject: str,
+        experiment_key: str,
+        experiment_config: ExperimentConfigurationDto,
+    ):
+        shard = get_shard(
+            "exposure-{}-{}".format(subject, experiment_key),
+            experiment_config.subject_shards,
+        )
+        return (
+            shard
+            <= experiment_config.percent_exposure * experiment_config.subject_shards
+        )

eppo_client/config.py

@@ -0,0 +1,11 @@
+from eppo_client.base_model import SdkBaseModel
+
+from eppo_client.validation import validate_not_blank
+
+
+class Config(SdkBaseModel):
+    api_key: str
+    base_url: str = "https://eppo.cloud/api"
+
+    def _validate(self):
+        validate_not_blank("api_key", self.api_key)

eppo_client/configuration_requestor.py

@@ -0,0 +1,25 @@
+from typing import List, Optional
+from eppo_client.base_model import SdkBaseModel
+
+from eppo_client.shard import ShardRange
+
+
+class VariationDto(SdkBaseModel):
+    name: str
+    shard_range: ShardRange
+
+
+class ExperimentConfigurationDto(SdkBaseModel):
+    subject_shards: int
+    percent_exposure: float
+    enabled: bool
+    variations: List[VariationDto]
+    name: str
+
+
+class ExperimentConfigurationRequestor:
+    def get_configuration(
+        self, experiment_key: str
+    ) -> Optional[ExperimentConfigurationDto]:
+        # TODO: implement this method
+        return None

eppo_client/example.py

@@ -0,0 +1,20 @@
+import hashlib
+
+from eppo_client.base_model import SdkBaseModel
+
+
+def get_shard(input: str, subject_shards: int):
+    hash_output = hashlib.md5(input.encode("utf-8")).hexdigest()
+    # get the first 4 bytes of the md5 hex string and parse it using base 16
+    # (8 hex characters represent 4 bytes, e.g. 0xffffffff represents the max 4-byte integer)
+    int_from_hash = int(hash_output[0:8], 16)
+    return int_from_hash % subject_shards
+
+
+class ShardRange(SdkBaseModel):
+    start: int
+    end: int
+
+
+def is_in_shard_range(shard: int, range: ShardRange) -> bool:
+    return shard >= range.start and shard < range.end

eppo_client/shard.py

@@ -0,0 +1,3 @@
+def validate_not_blank(field_name: str, field_value: str):
+    if field_value is None or field_value == "":
+        raise ValueError("Invalid value for {}: cannot be blank".format(field_name))

eppo_client/validation.py

@@ -1,3 +1,4 @@
 tox
 pytest
-mypy
+mypy
+google-cloud-storage