import unittest
from rest_framework import serializers

class DecimalFieldTest(unittest.TestCase):
    def test_decimal_field_1_1(self):
        class CustomSerializer(serializers.Serializer):
            input_num = serializers.DecimalField(min_value=1.1, decimal_places=2, max_digits=4)
        ser = CustomSerializer(data={"input_num": 1.1})
        ser.is_valid(raise_exception=True)

Running tests...
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E
======================================================================
ERROR [0.008s]: test_decimal_field_1_1
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Traceback (most recent call last):
    ser.is_valid(raise_exception=True)
  File "/root/.local/lib/python3.8/site-packages/rest_framework/serializers.py", line 228, in is_valid
    raise ValidationError(self.errors)
rest_framework.exceptions.ValidationError: {'input_num': [ErrorDetail(string='Ensure this value is greater than or equal to 1.1.', code='min_value')]}

>>> 1.1 > decimal.Decimal("1.1")
True

import unittest
import decimal
from rest_framework import serializers



class DecimalFieldTest(unittest.TestCase):
    def test_decimal_field_1_1(self):
        class CustomSerializer(serializers.Serializer):
            input_num = serializers.DecimalField(min_value=decimal.Decimal("1.1"), decimal_places=2, max_digits=4)
        ser = CustomSerializer(data={"input_num": 1.1})
        ser.is_valid(raise_exception=True)

Running tests...
----------------------------------------------------------------------
.
----------------------------------------------------------------------
Ran 1 test in 0.006s

OK