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Add support for __prepare__. #185

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Merged
merged 1 commit into from
Nov 3, 2018
Merged

Add support for __prepare__. #185

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8 changes: 7 additions & 1 deletion tests/snippets/metaclasses.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,9 @@ class MC(type):
classes = []
count = 0

def __prepare__(name, bases):
return {'prepared': True}

def __new__(cls, name, bases, namespace):
MC.classes.append(name)
return type.__new__(cls, name, bases, namespace)
Expand All @@ -16,10 +19,13 @@ def __new__(cls, count):
self.count = count
return self

class D(object, metaclass=MC):
class D(metaclass=MC):
pass

assert MC == type(C)
assert C == type(C())
assert MC.classes == ['C', 'D']
assert C().count == 2

assert C.prepared
assert D.prepared
16 changes: 13 additions & 3 deletions vm/src/builtins.rs
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Expand Up @@ -640,7 +640,19 @@ pub fn builtin_build_class_(vm: &mut VirtualMachine, mut args: PyFuncArgs) -> Py
let metaclass = args.get_kwarg("metaclass", vm.get_type());

bases.push(vm.context().object());
let namespace = vm.new_dict();
let bases = vm.context().new_tuple(bases);

// Prepare uses full __getattribute__ resolution chain.
let prepare_name = vm.new_str("__prepare__".to_string());
let prepare = vm.get_attribute(metaclass.clone(), prepare_name)?;
let namespace = vm.invoke(
prepare,
PyFuncArgs {
args: vec![name_arg.clone(), bases.clone()],
kwargs: vec![],
},
)?;

&vm.invoke(
function,
PyFuncArgs {
Expand All @@ -649,8 +661,6 @@ pub fn builtin_build_class_(vm: &mut VirtualMachine, mut args: PyFuncArgs) -> Py
},
);

let bases = vm.context().new_tuple(bases);

// Special case: __new__ must be looked up on the metaclass, not the meta-metaclass as
// per vm.call(metaclass, "__new__", ...)
let new = metaclass.get_attr("__new__").unwrap();
Expand Down
5 changes: 5 additions & 0 deletions vm/src/obj/objtype.rs
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Expand Up @@ -28,6 +28,7 @@ pub fn init(context: &PyContext) {
type_type.set_attr("__mro__", context.new_member_descriptor(type_mro));
type_type.set_attr("__class__", context.new_member_descriptor(type_new));
type_type.set_attr("__repr__", context.new_rustfunc(type_repr));
type_type.set_attr("__prepare__", context.new_rustfunc(type_prepare));
}

fn type_mro(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
Expand Down Expand Up @@ -300,6 +301,10 @@ fn type_repr(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
Ok(vm.new_str(format!("<class '{}'>", type_name)))
}

fn type_prepare(vm: &mut VirtualMachine, _args: PyFuncArgs) -> PyResult {
Ok(vm.new_dict())
}

#[cfg(test)]
mod tests {
use super::{linearise_mro, new};
Expand Down