Detect _param_names from __init__ signature (#867)

* Detect _param_names from __init__ signature

Signed-off-by: Fabrice Normandin <fabrice.normandin@gmail.com>

* Remove big NOTE block

Signed-off-by: Fabrice Normandin <fabrice.normandin@gmail.com>

src/orion/algo/base.py

@@ -16,6 +16,7 @@
 """
 import copy
 import hashlib
+import inspect
 import logging
 from abc import ABCMeta, abstractmethod
 
@@ -109,7 +110,16 @@ def __init__(self, space, **kwargs):
             kwargs,
         )
         self._space = space
-        self._param_names = list(kwargs.keys())
+        if kwargs:
+            param_names = list(kwargs)
+        else:
+            init_signature = inspect.signature(type(self))
+            param_names = [
+                name
+                for name, param in init_signature.parameters.items()
+                if name != "space" and param.kind != param.VAR_KEYWORD
+            ]
+        self._param_names = param_names
         # Instantiate tunable parameters of an algorithm
         for varname, param in kwargs.items():
             setattr(self, varname, param)

tests/unittests/algo/test_base.py

@@ -2,6 +2,9 @@
 # -*- coding: utf-8 -*-
 """Example usage and tests for :mod:`orion.algo.base`."""
 
+import pytest
+
+from orion.algo.base import BaseAlgorithm
 from orion.algo.space import Integer, Real, Space
 from orion.core.utils import backward, format_trials
 
@@ -108,3 +111,35 @@ def test_is_done_max_trials(monkeypatch, dumbalgo):
 
     dumbalgo.max_trials = 4
     assert algo.is_done
+
+
+@pytest.mark.parametrize("pass_to_super", [True, False])
+def test_arg_names(pass_to_super: bool):
+    """Test that the `_arg_names` can be determined programmatically when the args aren't passed to
+    `super().__init__(space, **kwargs)`.
+
+    Also checks that the auto-generated configuration dict acts the same way.
+    """
+
+    class SomeAlgo(BaseAlgorithm):
+        def __init__(self, space, foo: int = 123, bar: str = "heyo"):
+            if pass_to_super:
+                super().__init__(space, foo=foo, bar=bar)
+            else:
+                super().__init__(space)
+                self.foo = foo
+                self.bar = bar
+            # Param names should be correct, either way.
+            assert self._param_names == ["foo", "bar"]
+            # Attributes should be set correctly either way:
+            assert self.foo == foo
+            assert self.bar == bar
+
+    space = Space(x=Real("yolo1", "uniform", 1, 4))
+    algo = SomeAlgo(space, foo=111, bar="barry")
+    assert algo.configuration == {
+        "somealgo": {
+            "bar": "barry",
+            "foo": 111,
+        }
+    }