fix: expression hashing and repr (#39)

* fix: expression hashing and repr

* test: add tests

src/app_model/expressions/_expressions.py

@@ -26,8 +26,8 @@
 from __future__ import annotations
 
 import ast
-import sys
 from typing import (
+    TYPE_CHECKING,
     Any,
     Callable,
     Dict,
@@ -55,6 +55,9 @@
 T2 = TypeVar("T2", bound=Union[ConstType, "Expr"])
 V = TypeVar("V", bound=ConstType)
 
+if TYPE_CHECKING:
+    from ._context_keys import ContextKey
+
 
 def parse_expression(expr: str) -> Expr:
     """Parse string expression into an :class:`Expr` instance.
@@ -190,9 +193,7 @@ def _serialize(self) -> str:
         return str(_ExprSerializer(self))
 
     def __repr__(self) -> str:
-        if sys.version_info >= (3, 9):
-            return ast.dump(self, indent=2)
-        return ast.dump(self)
+        return f"Expr.parse({str(self)!r})"
 
     @staticmethod
     def _cast(obj: Any) -> Expr:
@@ -313,9 +314,15 @@ def validate(cls, v: Any) -> Expr:
         return v if isinstance(v, Expr) else parse_expression(v)
 
     def __hash__(self) -> int:
-        return hash(self.__class__) + hash(
-            tuple(getattr(self, f) for f in self._fields)
-        )
+        _hash = hash(self.__class__)
+        for f in self._fields:
+            field = getattr(self, f)
+            if isinstance(field, list):
+                field = tuple(field)
+            if isinstance(field, set):
+                field = frozenset(field)
+            _hash += hash(field)
+        return _hash
 
 
 LOAD = ast.Load()
@@ -528,6 +535,9 @@ def __str__(self) -> str:
     def visit_Name(self, node: ast.Name) -> None:
         self.write(node.id)
 
+    def visit_ContextKey(self, node: ContextKey) -> None:
+        return self.visit_Name(node)
+
     def visit_Constant(self, node: ast.Constant) -> None:
         self.write(repr(node.value))
 

tests/test_context/test_context_keys.py

@@ -8,12 +8,15 @@
 
 
 def test_context_key_info():
-    ContextKey("default", "description", None, id="some_key")
+    key = ContextKey("default", "description", None, id="some_key")
     info = ContextKey.info()
     assert isinstance(info, list) and len(info)
     assert all(isinstance(x, ContextKeyInfo) for x in info)
     assert "some_key" in {x.key for x in info}
 
+    assert repr(key) == "Expr.parse('some_key')"
+    assert repr(key == 1) == "Expr.parse('some_key == 1')"
+
 
 def _adder(x: list) -> int:
     return sum(x)

tests/test_context/test_expressions.py

@@ -1,5 +1,4 @@
 import ast
-import sys
 from copy import deepcopy
 
 import pytest
@@ -15,7 +14,7 @@ def test_names():
     with pytest.raises(NameError):
         Name("n").eval()
 
-    assert repr(Name("n")) == "Name(id='n', ctx=Load())"
+    assert repr(Name("n")) == "Expr.parse('n')"
 
 
 def test_constants():
@@ -33,10 +32,7 @@ def test_constants():
     assert Constant(False).eval() is False
     assert Constant(None).eval() is None
 
-    if sys.version_info >= (3, 9):
-        assert repr(Constant(1)) == "Constant(value=1)"
-    else:
-        assert repr(Constant(1)) == "Constant(value=1, kind=None)"
+    assert repr(Constant(1)) == "Expr.parse('1')"
 
     # only {None, str, bytes, bool, int, float} allowed
     with pytest.raises(TypeError):
@@ -140,6 +136,8 @@ def test_comparison():
     assert Expr.not_in(Constant("a"), Constant("abcd")).eval() is False
     assert Constant("a").not_in(Constant("abcd")).eval() is False
 
+    assert repr(n > n2) == "Expr.parse('n > n2')"
+
 
 def test_iter_names():
     expr = "a if b in c else d > e"
@@ -232,3 +230,8 @@ def test_safe_eval():
 
     with pytest.raises(SyntaxError, match="Type 'Set' not supported"):
         safe_eval("{1,2,3}")
+
+
+@pytest.mark.parametrize("expr", GOOD_EXPRESSIONS)
+def test_hash(expr):
+    assert isinstance(hash(expr), int)