fix(unparser): eagerly unparse float constants to scientific notation (#15)

* fix(unparser): eagerly unparse float constants to scientific notation

* fix build

Author: jvllmr

Cargo.toml

@@ -13,7 +13,7 @@ rust-version = "1.72.1"
 transformer = []
 
 [dependencies]
-rustpython-ast = { version = ">=0.4.0" }
+rustpython-ast = { version = ">=0.4.0", features = ["rustpython-literal"] }
 rustpython-literal = ">=0.4.0"
 
 [dev-dependencies]

src/unparser.rs

@@ -1057,6 +1057,7 @@ impl Unparser {
     }
 
     fn _unparse_constant(&mut self, constant: &Constant) {
+        let inf_str = "1e309";
         return match constant {
             Constant::Tuple(values) => {
                 self.write_str("(");
@@ -1094,8 +1095,37 @@ impl Unparser {
                 self.write_str(&escaped);
             }
             Constant::None => self.write_str("None"),
-            Constant::Complex { real, imag: _ } => self.write_str(&real.to_string()),
-            Constant::Float(value) => self.write_str(&value.to_string()),
+            Constant::Complex { real, imag } => {
+                if real.is_infinite() || imag.is_infinite() {
+                    self.write_str(&constant.to_string().replace("inf", &inf_str));
+                } else {
+                    self.write_str(&constant.to_string());
+                }
+            }
+            Constant::Float(value) => {
+                if value.is_infinite() {
+                    self.write_str(inf_str);
+                } else {
+                    let mut str_value = value.to_string();
+                    if value.fract() == 0.0 {
+                        let mut trailing_zeroes = 0;
+                        while str_value.ends_with("0") {
+                            str_value.pop();
+                            trailing_zeroes += 1;
+                        }
+                        str_value = format!("{}e{}", str_value, trailing_zeroes);
+                    } else if str_value.starts_with(&format!("0.{}", "0".repeat(5))) {
+                        let mut trimmed = str_value[2..].to_owned();
+                        let mut factor = 1;
+                        while trimmed.starts_with("0") {
+                            trimmed = trimmed[1..].to_owned();
+                            factor += 1;
+                        }
+                        str_value = format!("{}e-{}", trimmed, factor);
+                    }
+                    self.write_str(&str_value);
+                }
+            }
         };
     }
 

test_files/constants.py

@@ -1,3 +1,17 @@
 escaped_string_expr = "'\"'''\"\"\"{}\\"
 escaped_unicode_expr = u"'\"'''\"\"\"{}\\"  # fmt: skip
 escaped_bytes_expr = b"'\"'''\"\"\"{}\\"
+
+
+# real code from yaml.constructor
+# https://github.com/yaml/pyyaml/blob/69c141adcf805c5ebdc9ba519927642ee5c7f639/lib/yaml/constructor.py#L265
+inf_value = 1e300
+
+# if inf_value would not be initialized in scientific notation
+# the following loop would run for a long time
+while inf_value != inf_value * inf_value:
+    inf_value *= inf_value
+
+scientific_fraction = 1e-69
+
+complex_number = 3 + 4j