In this short lecture we will be discussing the range function. We haven't developed a very deep level of knowledge of functions yet, but we can understand the basics of this simple (but extremely useful!) function.
range() allows us to create a list of numbers ranging from a starting point up to an ending point. We can also specify step size. Lets walk through a few examples:
In [7]:
range(0,10)
Out[7]:
In [8]:
x =range(0,10)
type(x)
Out[8]:
In [3]:
start = 0 #Default
stop = 20
x = range(start,stop)
In [4]:
x
Out[4]:
Great! Notice how it went up to 20, but doesn't actually produce 20. Just like in indexing. What about step size? We can specify that as a third argument:
In [5]:
x = range(start,stop,2)
#Show
x
Out[5]:
Awesome! Well thats it...or is it?
You might have been wondering, what happens if I want to use a huge range of numbers? Can my computer store that all in memory?
Great thinking! This is a dilemma that can be solve with the use of a generator. For a simplified explanation: A generator allows the generation of generated objects that are provided at that instance but does not store every instance generated into memory.
This means a generator would not create a list to generate like range() does, but instead provide a one time generation of the numbers in that range. Python 2 has a built-in range generator called xrange(). It is recommended to use xrange() for for loops in Python 2.
The good news is in Python 3, range() behaves as a generator and you don't need to worry about it. Let's see a quick example with xrange()
In [9]:
for num in range(10):
print num
In [10]:
for num in xrange(10):
print num
So the main takeaway here is for Python 2, if you are using range() in a way that you don't need to save the results in a list, use xrange() instead. For Python 3, use range() in any instance.
You should now have a good understanding of how to use range() in either version of Python.