Added test ensuring DecimalField accepts `2E+2` as 200 and validates

decimal place correctly.

rest_framework/fields.py

@@ -782,7 +782,8 @@ class DecimalField(Field):
             self.fail('invalid')
 
         sign, digittuple, exponent = value.as_tuple()
-        decimals = abs(exponent)
+        decimals = exponent * decimal.Decimal(-1) if exponent < 0 else 0
+        
         # digittuple doesn't include any leading zeros.
         digits = len(digittuple)
         if decimals > digits:

tests/test_fields.py

@@ -647,6 +647,7 @@ class TestDecimalField(FieldValues):
         0: Decimal('0'),
         12.3: Decimal('12.3'),
         0.1: Decimal('0.1'),
+        '2E+2': Decimal('200'),
     }
     invalid_inputs = (
         ('abc', ["A valid number is required."]),