How do you divide each element in a list by an int?
The way you tried first is actually directly possible with numpy:
import numpy
myArray = numpy.array([10,20,30,40,50,60,70,80,90])
myInt = 10
newArray = myArray/myInt
If you do such operations with long lists and especially in any sort of scientific computing project, I would really advise using numpy.
The idiomatic way would be to use list comprehension:
myList = [10,20,30,40,50,60,70,80,90]
myInt = 10
newList = [x / myInt for x in myList]
or, if you need to maintain the reference to the original list:
myList[:] = [x / myInt for x in myList]