RustPython · joshuamegnauth54 · May 15, 2026
diff --git a/Cargo.lock b/Cargo.lock
diff --git a/Cargo.toml b/Cargo.toml
@@ -49,7 +49,7 @@
 flamescope = { version = "0.1.2", optional = true }

 rustls = { workspace = true, optional = true }
 rustls-graviola = { workspace = true, optional = true }

 [target.'cfg(windows)'.dependencies]
 libc = { workspace = true }
@@ -306,6 +306,7 @@
 timsort = "0.1.2"
 tk-sys = { git = "https://github.com/arihant2math/tkinter.git", tag = "v0.2.0" }
 icu_casemap = "2"
+icu_decimal = "2"
 icu_locale = "2"
 icu_properties = "2"
 icu_normalizer = "2"

diff --git a/crates/common/src/str.rs b/crates/common/src/str.rs
@@ -615,50 +615,6 @@ macro_rules! ascii {
 }
 pub use ascii;
 
-// TODO: this should probably live in a crate like unic or unicode-properties
-const UNICODE_DECIMAL_VALUES: &[char] = &[
-    '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '٠', '١', '٢', '٣', '٤', '٥', '٦', '٧', '٨',
-    '٩', '۰', '۱', '۲', '۳', '۴', '۵', '۶', '۷', '۸', '۹', '߀', '߁', '߂', '߃', '߄', '߅', '߆', '߇',
-    '߈', '߉', '०', '१', '२', '३', '४', '५', '६', '७', '८', '९', '০', '১', '২', '৩', '৪', '৫', '৬',
-    '৭', '৮', '৯', '੦', '੧', '੨', '੩', '੪', '੫', '੬', '੭', '੮', '੯', '૦', '૧', '૨', '૩', '૪', '૫',
-    '૬', '૭', '૮', '૯', '୦', '୧', '୨', '୩', '୪', '୫', '୬', '୭', '୮', '୯', '௦', '௧', '௨', '௩', '௪',
-    '௫', '௬', '௭', '௮', '௯', '౦', '౧', '౨', '౩', '౪', '౫', '౬', '౭', '౮', '౯', '೦', '೧', '೨', '೩',
-    '೪', '೫', '೬', '೭', '೮', '೯', '൦', '൧', '൨', '൩', '൪', '൫', '൬', '൭', '൮', '൯', '෦', '෧', '෨',
-    '෩', '෪', '෫', '෬', '෭', '෮', '෯', '๐', '๑', '๒', '๓', '๔', '๕', '๖', '๗', '๘', '๙', '໐', '໑',
-    '໒', '໓', '໔', '໕', '໖', '໗', '໘', '໙', '༠', '༡', '༢', '༣', '༤', '༥', '༦', '༧', '༨', '༩', '၀',
-    '၁', '၂', '၃', '၄', '၅', '၆', '၇', '၈', '၉', '႐', '႑', '႒', '႓', '႔', '႕', '႖', '႗', '႘', '႙',
-    '០', '១', '២', '៣', '៤', '៥', '៦', '៧', '៨', '៩', '᠐', '᠑', '᠒', '᠓', '᠔', '᠕', '᠖', '᠗', '᠘',
-    '᠙', '᥆', '᥇', '᥈', '᥉', '᥊', '᥋', '᥌', '᥍', '᥎', '᥏', '᧐', '᧑', '᧒', '᧓', '᧔', '᧕', '᧖', '᧗',
-    '᧘', '᧙', '᪀', '᪁', '᪂', '᪃', '᪄', '᪅', '᪆', '᪇', '᪈', '᪉', '᪐', '᪑', '᪒', '᪓', '᪔', '᪕', '᪖',
-    '᪗', '᪘', '᪙', '᭐', '᭑', '᭒', '᭓', '᭔', '᭕', '᭖', '᭗', '᭘', '᭙', '᮰', '᮱', '᮲', '᮳', '᮴', '᮵',
-    '᮶', '᮷', '᮸', '᮹', '᱀', '᱁', '᱂', '᱃', '᱄', '᱅', '᱆', '᱇', '᱈', '᱉', '᱐', '᱑', '᱒', '᱓', '᱔',
-    '᱕', '᱖', '᱗', '᱘', '᱙', '꘠', '꘡', '꘢', '꘣', '꘤', '꘥', '꘦', '꘧', '꘨', '꘩', '꣐', '꣑', '꣒', '꣓',
-    '꣔', '꣕', '꣖', '꣗', '꣘', '꣙', '꤀', '꤁', '꤂', '꤃', '꤄', '꤅', '꤆', '꤇', '꤈', '꤉', '꧐', '꧑', '꧒',
-    '꧓', '꧔', '꧕', '꧖', '꧗', '꧘', '꧙', '꧰', '꧱', '꧲', '꧳', '꧴', '꧵', '꧶', '꧷', '꧸', '꧹', '꩐', '꩑',
-    '꩒', '꩓', '꩔', '꩕', '꩖', '꩗', '꩘', '꩙', '꯰', '꯱', '꯲', '꯳', '꯴', '꯵', '꯶', '꯷', '꯸', '꯹', '０',
-    '１', '２', '３', '４', '５', '６', '７', '８', '９', '𐒠', '𐒡', '𐒢', '𐒣', '𐒤', '𐒥', '𐒦', '𐒧',
-    '𐒨', '𐒩', '𑁦', '𑁧', '𑁨', '𑁩', '𑁪', '𑁫', '𑁬', '𑁭', '𑁮', '𑁯', '𑃰', '𑃱', '𑃲', '𑃳', '𑃴', '𑃵', '𑃶',
-    '𑃷', '𑃸', '𑃹', '𑄶', '𑄷', '𑄸', '𑄹', '𑄺', '𑄻', '𑄼', '𑄽', '𑄾', '𑄿', '𑇐', '𑇑', '𑇒', '𑇓', '𑇔', '𑇕',
-    '𑇖', '𑇗', '𑇘', '𑇙', '𑋰', '𑋱', '𑋲', '𑋳', '𑋴', '𑋵', '𑋶', '𑋷', '𑋸', '𑋹', '𑑐', '𑑑', '𑑒', '𑑓', '𑑔',
-    '𑑕', '𑑖', '𑑗', '𑑘', '𑑙', '𑓐', '𑓑', '𑓒', '𑓓', '𑓔', '𑓕', '𑓖', '𑓗', '𑓘', '𑓙', '𑙐', '𑙑', '𑙒', '𑙓',
-    '𑙔', '𑙕', '𑙖', '𑙗', '𑙘', '𑙙', '𑛀', '𑛁', '𑛂', '𑛃', '𑛄', '𑛅', '𑛆', '𑛇', '𑛈', '𑛉', '𑜰', '𑜱', '𑜲',
-    '𑜳', '𑜴', '𑜵', '𑜶', '𑜷', '𑜸', '𑜹', '𑣠', '𑣡', '𑣢', '𑣣', '𑣤', '𑣥', '𑣦', '𑣧', '𑣨', '𑣩', '𑱐', '𑱑',
-    '𑱒', '𑱓', '𑱔', '𑱕', '𑱖', '𑱗', '𑱘', '𑱙', '𑵐', '𑵑', '𑵒', '𑵓', '𑵔', '𑵕', '𑵖', '𑵗', '𑵘', '𑵙', '𖩠',
-    '𖩡', '𖩢', '𖩣', '𖩤', '𖩥', '𖩦', '𖩧', '𖩨', '𖩩', '𖭐', '𖭑', '𖭒', '𖭓', '𖭔', '𖭕', '𖭖', '𖭗', '𖭘', '𖭙',
-    '𝟎', '𝟏', '𝟐', '𝟑', '𝟒', '𝟓', '𝟔', '𝟕', '𝟖', '𝟗', '𝟘', '𝟙', '𝟚', '𝟛', '𝟜', '𝟝', '𝟞', '𝟟', '𝟠',
-    '𝟡', '𝟢', '𝟣', '𝟤', '𝟥', '𝟦', '𝟧', '𝟨', '𝟩', '𝟪', '𝟫', '𝟬', '𝟭', '𝟮', '𝟯', '𝟰', '𝟱', '𝟲', '𝟳',
-    '𝟴', '𝟵', '𝟶', '𝟷', '𝟸', '𝟹', '𝟺', '𝟻', '𝟼', '𝟽', '𝟾', '𝟿', '𞥐', '𞥑', '𞥒', '𞥓', '𞥔', '𞥕', '𞥖',
-    '𞥗', '𞥘', '𞥙',
-];
-
-#[must_use]
-pub fn char_to_decimal(ch: char) -> Option<u8> {
-    UNICODE_DECIMAL_VALUES
-        .binary_search(&ch)
-        .ok()
-        .map(|i| (i % 10) as u8)
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;

diff --git a/crates/vm/Cargo.toml b/crates/vm/Cargo.toml
@@ -81,6 +81,7 @@ timsort = { workspace = true }
 
 ## unicode stuff
 icu_casemap = { workspace = true }
+icu_decimal = { workspace = true }
 icu_locale = { workspace = true }
 icu_properties = { workspace = true }
 writeable = { workspace = true }

diff --git a/crates/vm/src/builtins/float.rs b/crates/vm/src/builtins/float.rs
@@ -14,13 +14,16 @@ use crate::{
     },
     protocol::PyNumberMethods,
     types::{AsNumber, Callable, Comparable, Constructor, Hashable, PyComparisonOp, Representable},
+    utils::SliceFmtWriter,
 };
 use core::cell::Cell;
 use core::ptr::NonNull;
+use icu_decimal::input::Decimal;
 use malachite_bigint::{BigInt, ToBigInt};
 use num_complex::Complex64;
 use num_traits::{Signed, ToPrimitive, Zero};
 use rustpython_common::int::float_to_ratio;
+use writeable::Writeable;
 
 #[pyclass(module = false, name = "float")]
 #[derive(Debug, Copy, Clone, PartialEq)]
@@ -206,26 +209,28 @@ impl Constructor for PyFloat {
 }
 
 fn float_from_string(val: PyObjectRef, vm: &VirtualMachine) -> PyResult<f64> {
-    let (bytearray, buffer, buffer_lock, mapped_string);
+    let (bytearray, buffer, buffer_lock);
+    let mut mapped_str_buf = [0u8; 1024];
     let b = if let Some(s) = val.downcast_ref::<PyStr>() {
         use crate::common::str::PyKindStr;
         match s.as_str_kind() {
             PyKindStr::Ascii(s) => s.trim().as_bytes(),
             PyKindStr::Utf8(s) => {
-                mapped_string = s
-                    .trim()
-                    .chars()
-                    .map(|c| {
-                        if let Some(n) = rustpython_common::str::char_to_decimal(c) {
-                            char::from_digit(n.into(), 10).unwrap()
-                        } else if c.is_whitespace() {
-                            ' '
+                match Decimal::try_from_str(s.trim()) {
+                    Ok(decimal) => {
+                        let mut writer = SliceFmtWriter::new(&mut mapped_str_buf);
+                        if decimal.write_to(&mut writer).is_err() {
+                            s.as_bytes()
                         } else {
-                            c
+                            let written = writer.written();
+                            &mapped_str_buf[..written]
                         }
-                    })
-                    .collect::<String>();
-                mapped_string.as_bytes()
+                    }
+                    Err(_) => {
+                        // Let the string fail parsing below
+                        s.as_bytes()
+                    }
+                }
             }
             // if there are surrogates, it's not gonna parse anyway,
             // so we can just choose a known bad value

diff --git a/crates/vm/src/utils.rs b/crates/vm/src/utils.rs
@@ -87,3 +87,43 @@ impl fmt::Write for VecFmtWriter {
         Ok(())
     }
 }
+
+/// Wrapper around a bytes slice that implements [`fmt::Write`].
+///
+/// # Errors
+/// [`fmt::Error`] is returned if the string doesn't fit into the internal buffer. This
+/// implementation writes as many bytes as can fit before returning an error.
+/// Check [`Self::remainder`] if the amount of bytes that can be written is important.
+pub(crate) struct SliceFmtWriter<'slice> {
+    buf: &'slice mut [u8],
+    written: usize,
+}
+
+impl<'slice> SliceFmtWriter<'slice> {
+    pub(crate) const fn new(buf: &'slice mut [u8]) -> Self {
+        Self { buf, written: 0 }
+    }
+
+    /// Amount of space left in the internal buffer.
+    pub(crate) const fn remainder(&self) -> usize {
+        self.buf.len() - self.written
+    }
+
+    /// Amount of bytes written to the internal buffer.
+    pub(crate) const fn written(&self) -> usize {
+        self.written
+    }
+}
+
+impl fmt::Write for SliceFmtWriter<'_> {
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        let to_copy = self.remainder().min(s.len());
+        self.buf[self.written..self.written + to_copy].copy_from_slice(&s.as_bytes()[..to_copy]);
+        self.written += to_copy;
+        if to_copy == s.len() {
+            Ok(())
+        } else {
+            Err(fmt::Error)
+        }
+    }
+}