#!/usr/bin/env python
# coding: utf-8

# #range()
# 
# 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)


# In[8]:


x =range(0,10)
type(x)


# In[3]:


start = 0 #Default
stop = 20 
x = range(start,stop)


# In[4]:


x


# 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


# Awesome! Well thats it...or is it?

# ### <font color='red'>Python 3 Alert!</font>
# 
# 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.