RustPython
diff --git a/‎common/src/format.rs‎
Lines changed: 18 additions & 12 deletions b/‎common/src/format.rs‎
Lines changed: 18 additions & 12 deletions
diff --git a/‎extra_tests/snippets/builtin_format.py‎
Lines changed: 2 additions & 0 deletions b/‎extra_tests/snippets/builtin_format.py‎
Lines changed: 2 additions & 0 deletions
diff --git a/‎vm/src/builtins/float.rs‎
Lines changed: 5 additions & 6 deletions b/‎vm/src/builtins/float.rs‎
Lines changed: 5 additions & 6 deletions
@@ -422,10 +422,11 @@ impl FormatSpec {
         }
     }
 
-    pub fn format_float(&self, num: f64) -> Result<String, &'static str> {
+    pub fn format_float(&self, num: f64) -> Result<String, String> {
+        self.validate_format(FormatType::FixedPointLower)?;
         let precision = self.precision.unwrap_or(6);
         let magnitude = num.abs();
-        let raw_magnitude_str: Result<String, &'static str> = match self.format_type {
+        let raw_magnitude_str: Result<String, String> = match self.format_type {
             Some(FormatType::FixedPointUpper) => Ok(float_ops::format_fixed(
                 precision,
                 magnitude,
@@ -436,17 +437,21 @@ impl FormatSpec {
                 magnitude,
                 float_ops::Case::Lower,
             )),
-            Some(FormatType::Decimal) => Err("Unknown format code 'd' for object of type 'float'"),
-            Some(FormatType::Binary) => Err("Unknown format code 'b' for object of type 'float'"),
-            Some(FormatType::Octal) => Err("Unknown format code 'o' for object of type 'float'"),
-            Some(FormatType::HexLower) => Err("Unknown format code 'x' for object of type 'float'"),
-            Some(FormatType::HexUpper) => Err("Unknown format code 'X' for object of type 'float'"),
-            Some(FormatType::String) => Err("Unknown format code 's' for object of type 'float'"),
-            Some(FormatType::Character) => {
-                Err("Unknown format code 'c' for object of type 'float'")
+            Some(FormatType::Decimal)
+            | Some(FormatType::Binary)
+            | Some(FormatType::Octal)
+            | Some(FormatType::HexLower)
+            | Some(FormatType::HexUpper)
+            | Some(FormatType::String)
+            | Some(FormatType::Character) => {
+                let ch = char::from(self.format_type.as_ref().unwrap());
+                Err(format!(
+                    "Unknown format code '{}' for object of type 'float'",
+                    ch
+                ))
             }
             Some(FormatType::Number) => {
-                Err("Format code 'n' for object of type 'float' not implemented yet")
+                Err("Format code 'n' for object of type 'float' not implemented yet".to_owned())
             }
             Some(FormatType::GeneralFormatUpper) => {
                 let precision = if precision == 0 { 1 } else { precision };
@@ -513,6 +518,7 @@ impl FormatSpec {
         };
         let magnitude_str = self.add_magnitude_separators(raw_magnitude_str?, sign_str);
         self.format_sign_and_align(&magnitude_str, sign_str, FormatAlign::Right)
+            .map_err(|msg| msg.to_owned())
     }
 
     #[inline]
@@ -574,7 +580,7 @@ impl FormatSpec {
             | Some(FormatType::ExponentUpper)
             | Some(FormatType::ExponentLower)
             | Some(FormatType::Percentage) => match num.to_f64() {
-                Some(float) => return self.format_float(float).map_err(|msg| msg.to_owned()),
+                Some(float) => return self.format_float(float),
                 _ => Err("Unable to convert int to float".to_owned()),
             },
             None => self.format_int_radix(magnitude, 10),
 
@@ -68,3 +68,5 @@ def test_zero_padding():
 assert f"{1234567:.6G}" == "1.23457E+06"
 assert_raises(ValueError, "{:,o}".format, 1, _msg="ValueError: Cannot specify ',' with 'o'.")
 assert_raises(ValueError, "{:_n}".format, 1, _msg="ValueError: Cannot specify '_' with 'n'.")
+assert_raises(ValueError, "{:,o}".format, 1.0, _msg="ValueError: Cannot specify ',' with 'o'.")
+assert_raises(ValueError, "{:_n}".format, 1.0, _msg="ValueError: Cannot specify '_' with 'n'.")
@@ -189,12 +189,11 @@ fn float_from_string(val: PyObjectRef, vm: &VirtualMachine) -> PyResult<f64> {
 impl PyFloat {
     #[pymethod(magic)]
     fn format(&self, spec: PyStrRef, vm: &VirtualMachine) -> PyResult<String> {
-        match FormatSpec::parse(spec.as_str())
-            .and_then(|format_spec| format_spec.format_float(self.value))
-        {
-            Ok(string) => Ok(string),
-            Err(err) => Err(vm.new_value_error(err.to_string())),
-        }
+        let format_spec =
+            FormatSpec::parse(spec.as_str()).map_err(|msg| vm.new_value_error(msg.to_owned()))?;
+        format_spec
+            .format_float(self.value)
+            .map_err(|msg| vm.new_value_error(msg))
     }
 
     #[pystaticmethod(magic)]