params: Use ast.literal_eval for python params.

Add unit tests for `parse_py`

Closes  #6953

tests/unit/utils/serialize/test_python.py

@@ -0,0 +1,45 @@
+import pytest
+
+from dvc.utils.serialize import parse_py
+
+
+@pytest.mark.parametrize(
+    "text,result",
+    [
+        ("BOOL = True", {"BOOL": True}),
+        ("INT = 5", {"INT": 5}),
+        ("FLOAT = 0.001", {"FLOAT": 0.001}),
+        ("STR = 'abc'", {"STR": "abc"}),
+        ("DICT = {'a': 1, 'b': 2}", {"DICT": {"a": 1, "b": 2}}),
+        ("LIST = [1, 2, 3]", {"LIST": [1, 2, 3]}),
+        ("SET = {1, 2, 3}", {"SET": {1, 2, 3}}),
+        ("TUPLE = (10, 100)", {"TUPLE": (10, 100)}),
+        ("NONE = None", {"NONE": None}),
+        ("UNARY_OP = -1", {"UNARY_OP": -1}),
+        (
+            """class TrainConfig:
+
+            EPOCHS = 70
+
+            def __init__(self):
+                self.layers = 5
+                self.layers = 9  # TrainConfig.layers param will be 9
+                bar = 3  # Will NOT be found since it's locally scoped
+            """,
+            {"TrainConfig": {"EPOCHS": 70, "layers": 9}},
+        ),
+    ],
+)
+def test_parse_valid_types(text, result):
+    assert parse_py(text, "foo") == result
+
+
+@pytest.mark.parametrize(
+    "text",
+    [
+        "CONSTRUCTOR = dict(a=1, b=2)",
+        "SUM = 1 + 2",
+    ],
+)
+def test_parse_invalid_types(text):
+    assert parse_py(text, "foo") == {}