From bc1c03407649a37a8a3c26b8d0cb355ab2fc128e Mon Sep 17 00:00:00 2001
From: Hasan Ramezani <hasan.r67@gmail.com>
Date: Sun, 23 Feb 2020 14:37:02 +0100
Subject: [PATCH] Fixed #28280 -- Prevented numberformat.format() from
 formatting large/tiny floats in scientific notation.

---
 django/utils/numberformat.py           |  3 +++
 tests/utils_tests/test_numberformat.py | 28 ++++++++++++++++++++++----
 2 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/django/utils/numberformat.py b/django/utils/numberformat.py
index 961a60e37d..3bfdb2ea52 100644
--- a/django/utils/numberformat.py
+++ b/django/utils/numberformat.py
@@ -26,6 +26,9 @@ def format(number, decimal_sep, decimal_pos=None, grouping=0, thousand_sep='',
         return mark_safe(number)
     # sign
     sign = ''
+    # Treat potentially very large/small floats as Decimals.
+    if isinstance(number, float) and 'e' in str(number).lower():
+        number = Decimal(str(number))
     if isinstance(number, Decimal):
 
         if decimal_pos is not None:
diff --git a/tests/utils_tests/test_numberformat.py b/tests/utils_tests/test_numberformat.py
index 83e7d271b5..201e2cfe87 100644
--- a/tests/utils_tests/test_numberformat.py
+++ b/tests/utils_tests/test_numberformat.py
@@ -55,10 +55,30 @@ class TestNumberFormat(SimpleTestCase):
         self.assertEqual(nformat(-2 * int_max, '.'), most_max2.format('-'))
 
     def test_float_numbers(self):
-        # A float without a fractional part (3.) results in a ".0" when no
-        # decimal_pos is given. Contrast that with the Decimal('3.') case in
-        # test_decimal_numbers which doesn't return a fractional part.
-        self.assertEqual(nformat(3., '.'), '3.0')
+        tests = [
+            (9e-10, 10, '0.0000000009'),
+            (9e-19, 2, '0.00'),
+            (.00000000000099, 0, '0'),
+            (.00000000000099, 13, '0.0000000000009'),
+            (1e16, None, '10000000000000000'),
+            (1e16, 2, '10000000000000000.00'),
+            # A float without a fractional part (3.) results in a ".0" when no
+            # decimal_pos is given. Contrast that with the Decimal('3.') case
+            # in test_decimal_numbers which doesn't return a fractional part.
+            (3., None, '3.0'),
+        ]
+        for value, decimal_pos, expected_value in tests:
+            with self.subTest(value=value, decimal_pos=decimal_pos):
+                self.assertEqual(nformat(value, '.', decimal_pos), expected_value)
+        # Thousand grouping behavior.
+        self.assertEqual(
+            nformat(1e16, '.', thousand_sep=',', grouping=3, force_grouping=True),
+            '10,000,000,000,000,000',
+        )
+        self.assertEqual(
+            nformat(1e16, '.', decimal_pos=2, thousand_sep=',', grouping=3, force_grouping=True),
+            '10,000,000,000,000,000.00',
+        )
 
     def test_decimal_numbers(self):
         self.assertEqual(nformat(Decimal('1234'), '.'), '1234')