Modifying the value of a float-like object

Christian Heimes lists at
Tue Apr 14 17:52:01 CEST 2009

Eric.Le.Bigot at wrote:
> Hello,
> Is there a way to easily build an object that behaves exactly like a
> float, but whose value can be changed?  The goal is to maintain a list
> [x, y,…] of these float-like objects, and to modify their value on the
> fly (with something like x.value = 3.14) so that any expression like "x
> +y" uses the new value.

Your approach doesn't follow the Python philosophy thus it's most likely
to fail. It is possible to implement a mutable float like object --
Python doesn't stop you from shooting yourself in the knee -- but please
don't harm yourself.

Python has an easy way to archive an equal goal:

data = [1.0, 2.0, -1.0, -7.0, 23.0]
for idx, value in enumerate(data):
    if value < 0.0:
        data[idx] = value**2

Important side note:
It's ok to modify elements of a list while iterating over the same list.
But you should not remove, append, insert or reorder the list while you
are iterating over it. It will lead to surprising effects.


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