On 2012-09-30 01:43, Jan Kaliszewski wrote:
Hello,
In http://docs.python.org/release/3.2.3/reference/expressions.html#in
we read: "[...] This can create the illusion of non-transitivity between
supported cross-type comparisons and unsupported comparisons. For
example, Decimal(2) == 2 and 2 == float(2) but Decimal(2) != float(2)."
(The same is in the 3.3 docs).
But:
Python 3.2.3 (default, Sep 10 2012, 18:14:40)
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more
information.
>>> import decimal
>>> decimal.Decimal(2) == float(2)
True
Is it a bug in the docs or in Python itself? (I checked that in 3.2,
but it may be true for 3.3 as well)
It's the same in Python 3.3:
>>> decimal.Decimal(2) == float(2)
True
Also:
>>> decimal.Decimal(0.1) == 0.1
True
>>> decimal.Decimal("0.1") == 0.1
False
This is because floats work in binary:
>>> decimal.Decimal(0.1) # from a float
Decimal('0.1000000000000000055511151231257827021181583404541015625')
>>> decimal.Decimal("0.1")
Decimal('0.1')
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