Add objsequence::{opt_,}len

Author: coolreader18

vm/src/builtins.rs

@@ -22,6 +22,7 @@ use crate::obj::objdict::PyDictRef;
 use crate::obj::objfunction::PyFunctionRef;
 use crate::obj::objint::{self, PyIntRef};
 use crate::obj::objiter;
+use crate::obj::objsequence;
 use crate::obj::objstr::{PyString, PyStringRef};
 use crate::obj::objtype::{self, PyClassRef};
 use crate::pyhash;
@@ -384,11 +385,8 @@ fn builtin_iter(iter_target: PyObjectRef, vm: &VirtualMachine) -> PyResult {
     objiter::get_iter(vm, &iter_target)
 }
 
-fn builtin_len(obj: PyObjectRef, vm: &VirtualMachine) -> PyResult {
-    let method = vm.get_method_or_type_error(obj.clone(), "__len__", || {
-        format!("object of type '{}' has no len()", obj.class().name)
-    })?;
-    vm.invoke(&method, PyFuncArgs::default())
+fn builtin_len(obj: PyObjectRef, vm: &VirtualMachine) -> PyResult<usize> {
+    objsequence::len(&obj, vm)
 }
 
 fn builtin_locals(vm: &VirtualMachine) -> PyDictRef {

vm/src/exceptions.rs

@@ -250,8 +250,6 @@ pub fn write_exception_inner<W: Write>(
             write_traceback_entry(output, traceback)?;
             tb = traceback.next.as_ref();
         }
-    } else {
-        writeln!(output, "No traceback set on exception")?;
     }
 
     let varargs = exc.args();

vm/src/obj/objsequence.rs

@@ -263,3 +263,33 @@ pub fn is_valid_slice_arg(
         Ok(None)
     }
 }
+
+pub fn opt_len(obj: &PyObjectRef, vm: &VirtualMachine) -> Option<PyResult<usize>> {
+    vm.get_method(obj.clone(), "__len__").map(|len| {
+        let len = vm.invoke(&len?, vec![])?;
+        let len = len
+            .payload_if_subclass::<PyInt>(vm)
+            .ok_or_else(|| {
+                vm.new_type_error(format!(
+                    "'{}' object cannot be interpreted as an integer",
+                    len.class().name
+                ))
+            })?
+            .as_bigint();
+        if len.is_negative() {
+            return Err(vm.new_value_error("__len__() should return >= 0".to_string()));
+        }
+        len.to_usize().ok_or_else(|| {
+            vm.new_overflow_error("cannot fit __len__() result into usize".to_string())
+        })
+    })
+}
+
+pub fn len(obj: &PyObjectRef, vm: &VirtualMachine) -> PyResult<usize> {
+    opt_len(obj, vm).unwrap_or_else(|| {
+        Err(vm.new_type_error(format!(
+            "object of type '{}' has no len()",
+            obj.class().name
+        )))
+    })
+}