I am working with
a = (1.,80.,5.)
aList = np.arange(a, a+a, a)
a is a tuple of floats. A tuple is a kind of structure that is kinda like a list, but is immutable (i.e. you cannot modify any of its components once it has been created). But, like a list it can be indexed.
In theory, some tuples have special names, for example a tuple of 2 is called a pair, a tuple of 3 is called a triplet etc (people don't necessarily call them that, but it helps a bit more to understand what a tuple is about). Because it's immutable, conceptually it is thought of more as a unique object, rather than as a collection of ones; for this reason it can also be validly used as a key to a dictionary (as opposed to lists which cannot).
To create a tuple, you create a comma-separated sequence of objects inside parentheses, i.e.
() (as opposed to brackets, i.e.
 that you would to create a list).
As for floats, the float
3.0 can also be written
3. for short.
numpy.arange function then creates a range by calling it using the components of the tuple as arguments. In your particular case, it will create a range of numbers from 1 to 80+5, at increments of 5.
A very cool use of tuples is that they can be expanded into a sequence of arguments to a function. e.g. if you had a tuple
a = (1.,10.,2.), and you wanted to call
numpy.arange(a, a, a), you could just do