Merge pull request RustPython#1551 from ChJR/feature/float-repr

Fix float.__repr__()

Author: windelbouwman

tests/snippets/floats.py

@@ -289,3 +289,14 @@
 assert float('nan').__ne__(float('nan')) is True
 assert float('nan').__eq__(float('inf')) is False
 assert float('nan').__ne__(float('inf')) is True
+
+assert float(1e15).__repr__() == "1000000000000000.0"
+assert float(1e16).__repr__() == "1e+16"
+assert float(1e308).__repr__() == "1e+308"
+assert float(1e309).__repr__() == "inf"
+assert float(1e-323).__repr__() == "1e-323"
+assert float(1e-324).__repr__() == "0.0"
+assert float(1e-5).__repr__() == "1e-05"
+assert float(1e-4).__repr__() == "0.0001"
+assert float(1.2345678901234567890).__repr__() == "1.2345678901234567"
+assert float(1.2345678901234567890e308).__repr__() == "1.2345678901234567e+308"

vm/src/obj/objfloat.rs

@@ -416,8 +416,20 @@ impl PyFloat {
 
     #[pymethod(name = "__repr__")]
     fn repr(&self, vm: &VirtualMachine) -> String {
-        if self.is_integer(vm) {
-            format!("{:.1?}", self.value)
+        let value = format!("{:e}", self.value);
+        if let Some(position) = value.find('e') {
+            let significand = &value[..position];
+            let exponent = &value[position + 1..];
+            let exponent = exponent.parse::<i32>().unwrap();
+            if exponent < 16 && exponent > -5 {
+                if self.is_integer(vm) {
+                    format!("{:.1?}", self.value)
+                } else {
+                    self.value.to_string()
+                }
+            } else {
+                format!("{}e{:+#03}", significand, exponent)
+            }
         } else {
             self.value.to_string()
         }