From 25087f91da8e12f53a2d6eae8f19fb077fc23c1c Mon Sep 17 00:00:00 2001
From: ANSHUL SINGH <72524975+ekanshul@users.noreply.github.com>
Date: Thu, 5 Nov 2026 22:26:30 +0530
Subject: [PATCH] Fix intcomma() digit loss on large decimal strings

Fixes https://github.com/python-humanize/humanize/issues/496

intcomma() converted decimal strings with float(value), losing precision
on large values (e.g. '1234567890123456.78' -> '...456.8').
Keep the exact string for the ndigits=None path and use Decimal when
ndigits is given, preserving all input digits.

Co-authored-by: CommandCodeBot <noreply@commandcode.ai>
---
 src/humanize/number.py | 20 ++++++++++++++++++--
 tests/test_number.py   |  2 ++
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/src/humanize/number.py b/src/humanize/number.py
index 52a5356a..36f06669 100644
--- a/src/humanize/number.py
+++ b/src/humanize/number.py
@@ -175,16 +175,20 @@ def intcomma(value: NumberOrString, ndigits: int | None = None) -> str:
         str: String containing commas every three digits.
     """
     import math
+    from decimal import Decimal
 
     thousands_sep = thousands_separator()
     decimal_sep = decimal_separator()
+    is_str_decimal = False
     try:
         if isinstance(value, str):
             value = value.replace(thousands_sep, "").replace(decimal_sep, ".")
             if not math.isfinite(float(value)):
                 return _format_not_finite(float(value))
             if "." in value:
-                value = float(value)
+                # Keep the exact decimal string to avoid float() rounding
+                # large values, e.g. '1234567890123456.78'.
+                is_str_decimal = True
             else:
                 value = int(value)
         elif not isinstance(value, int):
@@ -195,9 +199,21 @@ def intcomma(value: NumberOrString, ndigits: int | None = None) -> str:
         return str(value)
 
     if ndigits is not None:
+        if is_str_decimal:
+            value = Decimal(value)
         result = f"{value:,.{ndigits}f}"
     else:
-        result = f"{value:,}"
+        if is_str_decimal:
+            # Format the original digit string directly so no precision is lost.
+            int_part, _, frac_part = value.partition(".")
+            sign = ""
+            if int_part.startswith(("-", "+")):
+                sign, int_part = int_part[0], int_part[1:]
+            int_part = int_part.lstrip("0") or "0"
+            grouped = f"{int(int_part):,}" if int_part else "0"
+            result = f"{sign}{grouped}.{frac_part}" if frac_part else f"{sign}{grouped}"
+        else:
+            result = f"{value:,}"
     if thousands_sep != "," or decimal_sep != ".":
         result = result.translate(str.maketrans(",.", thousands_sep + decimal_sep))
     return result
diff --git a/tests/test_number.py b/tests/test_number.py
index 5fb12fa6..10888e8a 100644
--- a/tests/test_number.py
+++ b/tests/test_number.py
@@ -53,6 +53,8 @@ def test_ordinal(test_input: str, expected: str) -> None:
         (["10311"], "10,311"),
         (["1000000"], "1,000,000"),
         (["1234567.1234567"], "1,234,567.1234567"),
+        (["1234567890123456.78"], "1,234,567,890,123,456.78"),
+        (["1234567890123456.78", 2], "1,234,567,890,123,456.78"),
         (["1234567.1234567", 0], "1,234,567"),
         (["1234567.1234567", 1], "1,234,567.1"),
         (["1234567.1234567", 10], "1,234,567.1234567000"),