New submission from Cal Leeming:
Hello,
Today I came up against a strange problem where collisions were being
encountered after less than 1mil iterations when attempting to use
random.random().
After much digging, the problem was because I was casting my float to a string,
and this was
Serhiy Storchaka added the comment:
http://docs.python.org/2/tutorial/floatingpoint.html
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nosy: +serhiy.storchaka
resolution: - invalid
status: open - pending
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Python tracker rep...@bugs.python.org
http://bugs.python.org/issue16609
Cal Leeming added the comment:
As stated before, I have already read this document.
This ticket is specifically about making users aware of this behaviour in the
form of a documentation update on the random.random() docs.
The link you provided does not exactly make this very clear.
Mark Dickinson added the comment:
The `random` module docs are not the right place to add notes about general
floating-point arithmetic behaviour.
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nosy: +mark.dickinson
___
Python tracker rep...@bugs.python.org
http://bugs.python.org/issue16609
Cal Leeming added the comment:
Normally I would concur, but casting random.random() to a string is commonly
used, and people aren't going to read the entire floating point arithmetic page
to figure this out. And even if they do, that page still doesn't make it
entirely obvious at first read.
R. David Murray added the comment:
In fact it has been changed. In Python3 you get:
x = 0.88022393777095409
x
0.8802239377709541
str(x)
'0.8802239377709541'
Even in 2.7 you would get the above repr, not the one you showed. This is
because 2.7 and 3.3 use the shortest repr described in
Cal Leeming added the comment:
Many thanks for your lengthy response David.
Sorry, my initial bug report stated it was Python 2.7. The tests I performed
were actually on Python 2.6.6.
I will take a look at how to contribute documentation updates, and once I've
familiarized myself with it
Mark Dickinson added the comment:
It is notable that this behaviour isn't described anywhere that I can find in
the library manual or the reference manual. As David says, it applies only to
2.7; in 3.2 and later, `str` and `repr` are identical.
a glossary entry be added for 'floating
