"Variable variable name" or "variable lvalue"

[Peter Otten]

mfglinux wrote:

> Hello to everybody
> 
> I would like to know how to declare in python a "variable name" that
> it is in turn a variable
> In bash shell I would wrote sthg like:
> 
> for x in `seq 1 3`
> do
>   M$i=Material(x)  #Material is a python class
> done

In Python you would build a list instead of inventing variable names:

    numbers = [12.5, 25, 12.5]
    materials = []
    for x in numbers:
        materials.append(Material(x))


> Why I need this? Cause I have a python module that obliges me to build
> a variable called Period, which should have a variable name of
> summands (depends on the value of x)
> 
> #Let's say x=3, then Period definition is
> Period=Slab(Material1(12.5)+Material2(25)+Material3(12.5)) #Slab is a
> python class
> 
> I dont know how to automatize last piece of code for any x

You can use another loop to to "sum" over the materials and then feed the
result to the Slab constructor:

    accu = materials[0]
    for material in materials[1:]:
        accu += material
    period = Slab(accu)

If you want to simplify things somewhat you can merge the two loops into
one:

    numbers = [12.5, 25, 12.5]
    accu = Material(numbers[0])
    for x in numbers[1:]:
        accu += Material(x)
    period = Slab(accu)

Or you try your hands on a bit of functional programming:

    from operator import add
    numbers = [12.5, 25, 12.5]
    period = Slab(reduce(add, (Material(x) for x in numbers)))

Peter