You can't have brackets ( and ) as part of the variable name as this syntax is used to call a function. You are effectively trying to call a function rdf12 with the values of i.
If you name your variables rdf12_0, rdf12_1, etc you may be able to access them through the locals() function which returns a dict of local variable declarations, however I believe making modifications to this dict is not guaranteed to work and as such is a really bad idea.
>>> rdf12_0 = 0
>>> lcls = locals()
>>> print(lcls['rdf12_0'])
0
>>> name = 'rdf12_' + str(0)
>>> lcls[name] = 34
>>> rdf12_0
34
I would suggest instead, storing your values in a list:
>>> rdf12 = [34, 12, 9, 97]
>>> rdf12[0]
34
>>> rdf12[1]
12
>>> for i in rdf12:
... print(i)
...
34
12
9
97