cleanup string validation a little (#624)

Author: samuelcolvin

src/input/input_python.rs

@@ -187,26 +187,22 @@ impl<'a> Input<'a> for PyAny {
     }
 
     fn strict_str(&'a self) -> ValResult<EitherString<'a>> {
-        if let Ok(py_str) = self.downcast::<PyString>() {
-            if is_builtin_str(py_str) {
-                Ok(py_str.into())
-            } else {
-                Err(ValError::new(ErrorType::StringSubType, self))
-            }
+        if let Ok(py_str) = <PyString as PyTryFrom>::try_from_exact(self) {
+            Ok(py_str.into())
+        } else if PyString::is_type_of(self) {
+            Err(ValError::new(ErrorType::StringSubType, self))
         } else {
             Err(ValError::new(ErrorType::StringType, self))
         }
     }
 
     fn lax_str(&'a self) -> ValResult<EitherString<'a>> {
-        if let Ok(py_str) = self.downcast::<PyString>() {
-            if is_builtin_str(py_str) {
-                Ok(py_str.into())
-            } else {
-                // force to a rust string to make sure behaviour is consistent whether or not we go via a
-                // rust string in StrConstrainedValidator - e.g. to_lower
-                Ok(py_string_str(py_str)?.into())
-            }
+        if let Ok(py_str) = <PyString as PyTryFrom>::try_from_exact(self) {
+            Ok(py_str.into())
+        } else if let Ok(py_str) = self.downcast::<PyString>() {
+            // force to a rust string to make sure behaviour is consistent whether or not we go via a
+            // rust string in StrConstrainedValidator - e.g. to_lower
+            Ok(py_string_str(py_str)?.into())
         } else if let Ok(bytes) = self.downcast::<PyBytes>() {
             let str = match from_utf8(bytes.as_bytes()) {
                 Ok(s) => s,
@@ -647,10 +643,6 @@ fn maybe_as_string(v: &PyAny, unicode_error: ErrorType) -> ValResult<Option<Cow<
     }
 }
 
-fn is_builtin_str(py_str: &PyString) -> bool {
-    py_str.get_type().is(PyString::type_object(py_str.py()))
-}
-
 #[cfg(PyPy)]
 static DICT_KEYS_TYPE: pyo3::once_cell::GILOnceCell<Py<PyType>> = pyo3::once_cell::GILOnceCell::new();
 

tests/benchmarks/test_micro_benchmarks.py

@@ -1314,6 +1314,7 @@ class SomeStrEnum(str, Enum):
 LARGE_STR_PREFIX = 'a' * 50
 
 
+@pytest.mark.benchmark(group='validate_literal')
 @pytest.mark.parametrize(
     'allowed_values,input,expected_val_res',
     [