eric.le.bi...@spectro.jussieu.fr wrote:
It looks like what is needed here are a kind of "mutable float". Is
there a simple way of creating such a type? I don't mind changing the
value through x.value =.23 instead of x = 1.23... :)
On Apr 14, 3:03 pm, eric.le.bi...@spectro.jussieu.fr 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 =.14) so that any expression like "x
+y" uses the new value.
I thought of two solutions, both of which I can't make to work:
1) Use a class that inherits from float. This takes care of the
"behave like float" part. But is it possible to change the value of
the float associated with an instance? That is, is it possible to
do: "x =yFloat(1.23); x.change_value(3.14)" so that x's float value
becomes 3.14?
2) The other possibility I thought of was: use a class that defines a
'value' member (x.value). This takes care of the "value can be
changed" part. But is it possible/easy to make it fully behave like a
float (including when passed to functions like math.sin)?
Alternatively, I'd be happy with a way of handling numerical
uncertainties in Python calculations (such as in "calculate the value
and uncertainty of a*sin(b) knowing that a=0 +/- 0.1 and b=1.00 +/-
0.01").
Any idea would be much appreciated!
The answer to your original question is no. If the value can be changed, then
it doesn't behave like a float. And that's not just a pedantic answer, it's a
serious consideration.
You have to decide what characteristics of a float you need to mimic, and which ones you
don't care about, and which ones you want to change. Only after having a pretty good
handle on those answers can you pick a "best" implementation.
Let's call this new type a nfloat, and let's assume you have a function that
returns one. That might be a constructor, but it may not, so we're keeping our
options open.
myval = newfunction(42.0)
What do you want to happen when you execute b = myval ? Presumably
you want them to be "equal" but in what sense? Suppose you then change
one of them with your suggested attribute/method.
myval.value = newfunction("aaa")
is b the same as it was (like a float would be), or is b also changed?
Do you need lots of functions to work on one of these nfloats, or could
you use them as follows:
sin( b.value )
Instead of using .value to change the underlying float, how about if you
use [0] ? Just use a list of size 1.
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