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From: Chris Angelico <rosuav@gmail.com>
Newsgroups: comp.lang.python
Subject: Re: Question about math.pi is mutable
Date: Fri, 6 Nov 2015 21:30:16 +1100
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On Fri, Nov 6, 2015 at 1:33 PM, wangq@travelsky.com <wangq@travelsky.com> w=
rote:
> Hello, python-list guys:
>
>     I am a newbie of python from Beijing. China.
>     I have a question about "math.pi".
>     As you can see in the attachment, why i can modify "math.pi"?
>     (in "mathmodule.c" "pi" is a "static const double")
>
> Thank you in advance!
>
> Best Wishes=EF=BC=81

Simply because, in Python, virtually everything can be changed. You're
welcome to go in and say "math.pi =3D 3" if you like... and then you
accept the consequences of that.

There are times when you want to change these sorts of 'constants'.
For example, math.pi is a float; but if you're working with
decimal.Decimal everywhere, it might be useful to replace it with a
corresponding Decimal value:

math.pi =3D decimal.Decimal("3.14159265358979323")

And that's perfectly legal.

ChrisA