diff --git a/Lib/_pydecimal.py b/Lib/_pydecimal.py
index 0b40928ff8d109..0fa152c2a6f8ef 100644
--- a/Lib/_pydecimal.py
+++ b/Lib/_pydecimal.py
@@ -734,18 +734,23 @@ def from_float(cls, f):
"""
if isinstance(f, int): # handle integer inputs
- return cls(f)
- if not isinstance(f, float):
- raise TypeError("argument must be int or float.")
- if _math.isinf(f) or _math.isnan(f):
- return cls(repr(f))
- if _math.copysign(1.0, f) == 1.0:
- sign = 0
+ sign = 0 if f >= 0 else 1
+ k = 0
+ coeff = str(abs(f))
+ elif isinstance(f, float):
+ if _math.isinf(f) or _math.isnan(f):
+ return cls(repr(f))
+ if _math.copysign(1.0, f) == 1.0:
+ sign = 0
+ else:
+ sign = 1
+ n, d = abs(f).as_integer_ratio()
+ k = d.bit_length() - 1
+ coeff = str(n*5**k)
else:
- sign = 1
- n, d = abs(f).as_integer_ratio()
- k = d.bit_length() - 1
- result = _dec_from_triple(sign, str(n*5**k), -k)
+ raise TypeError("argument must be int or float.")
+
+ result = _dec_from_triple(sign, coeff, -k)
if cls is Decimal:
return result
else:
diff --git a/Lib/test/test_decimal.py b/Lib/test/test_decimal.py
index 59a17af278c052..48360d1baedb64 100644
--- a/Lib/test/test_decimal.py
+++ b/Lib/test/test_decimal.py
@@ -1185,6 +1185,16 @@ def test_wide_char_separator_decimal_point(self):
self.assertEqual(format(Decimal('100000000.123'), 'n'),
'100\u066c000\u066c000\u066b123')
+ def test_decimal_from_float_argument_type(self):
+ class A(self.decimal.Decimal):
+ def __init__(self, a):
+ self.a_type = type(a)
+ a = A.from_float(42.5)
+ self.assertEqual(self.decimal.Decimal, a.a_type)
+
+ a = A.from_float(42)
+ self.assertEqual(self.decimal.Decimal, a.a_type)
+
class CFormatTest(FormatTest):
decimal = C
class PyFormatTest(FormatTest):
diff --git a/Misc/NEWS b/Misc/NEWS
index eb870b7d48b76b..f650e5c605dc31 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,8 @@ What's New in Python 3.7.0 alpha 1?
Core and Builtins
-----------------
+- bpo-29534: Fixed different behaviour of Decimal.from_float() for _decimal and _pydecimal.
+
- bpo-29438: Fixed use-after-free problem in key sharing dict.
- Issue #29319: Prevent RunMainFromImporter overwriting sys.path[0].
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