float.__round__ for ndigits == 0

Author: youknowone

tests/snippets/floats.py

@@ -114,6 +114,14 @@
 assert math.trunc(1.2) == 1
 assert_raises(OverflowError, float('inf').__trunc__)
 assert_raises(ValueError, float('nan').__trunc__)
+assert 0.5.__round__() == 0.0
+assert 1.5.__round__() == 2.0
+assert 0.5.__round__(0) == 0.0
+assert 1.5.__round__(0) == 2.0
+assert 0.5.__round__(None) == 0.0
+assert 1.5.__round__(None) == 2.0
+assert_raises(OverflowError, float('inf').__round__)
+assert_raises(ValueError, float('nan').__round__)
 
 assert (1.7).real == 1.7
 assert (1.3).is_integer() == False

vm/src/obj/objfloat.rs

@@ -11,7 +11,7 @@ use crate::pyobject::{
 use crate::vm::VirtualMachine;
 use num_bigint::{BigInt, ToBigInt};
 use num_rational::Ratio;
-use num_traits::ToPrimitive;
+use num_traits::{ToPrimitive, Zero};
 
 #[pyclass(name = "float")]
 #[derive(Debug, Copy, Clone, PartialEq)]
@@ -387,8 +387,19 @@ impl PyFloat {
             OptionalArg::Missing => None,
             OptionalArg::Present(ref value) => {
                 if !vm.get_none().is(value) {
-                    // retrive int to implement it
-                    Some(vm.ctx.not_implemented())
+                    let ndigits = if objtype::isinstance(value, &vm.ctx.int_type()) {
+                        objint::get_value(value)
+                    } else {
+                        return Err(vm.new_type_error(format!(
+                            "TypeError: '{}' object cannot be interpreted as an integer",
+                            value.class().name
+                        )));
+                    };
+                    if ndigits.is_zero() {
+                        None
+                    } else {
+                        Some(ndigits)
+                    }
                 } else {
                     None
                 }