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

# # Numbers and more in Python!
# 
# In this lecture, we will learn about numbers in Python and how to use them.
# 
# We'll learn about the following topics:
# 
#     1.) Types of Numbers in Python
#     2.) Basic Arithmetic
#     3.) Differences between Python 2 vs 3 in division
#     4.) Object Assignment in Python

# ## Types of numbers
# 
# Python has various "types" of numbers (numeric literals). We'll mainly focus on integers and floating point numbers.
# 
# Integers are just whole numbers, positive or negative. For example: 2 and -2 are examples of integers.
# 
# Floating point numbers in Python are notable because they have a decimal point in them, or use an exponential (e) to define the number. For example 2.0 and -2.1 are examples of floating point numbers. 4E2 (4 times 10 to the power of 2) is also an example of a floating point number in Python.
# 
# Throughout this course we will be mainly working with integers or simple float number types.
# 
# Here is a table of the two main types we will spend most of our time working with some examples:

# <table>
# <tr>
#     <th>Examples</th> 
#     <th>Number "Type"</th>
# </tr>
# 
# <tr>
#     <td>1,2,-5,1000</td>
#     <td>Integers</td> 
# </tr>
# 
# <tr>
#     <td>1.2,-0.5,2e2,3E2</td> 
#     <td>Floating-point numbers</td> 
# </tr>
#  </table>

#  
#  
# Now let's start with some basic arithmetic.

# ### Basic Arithmetic

# In[1]:


# Addition
2+1


# In[2]:


# Subtraction
2-1


# In[3]:


# Multiplication
2*2


# In[4]:


# Division
3/2


# ### <font color='red'>Python 3 Alert!</font>
# 
# **Whoa! What just happened? Last time I checked, 3 divided by 2 is equal 1.5 not 1!**
# 
# The reason we get this result is because we are using Python 2. In Python 2, the / symbol performs what is known as "*classic*" division, this means that the decimal points are truncated (cut off). In Python 3 however, a single / performs "*true*" division. So you would get 1.5 if you had inputed 3/2 in Python 3.
# 
# So what do we do if we are using Python 2 to avoid this?
# 
# There are two options:
# 
# Specify one of the numbers to be a float:

# In[11]:


# Specifying one of the numbers as a float
3.0/2


# In[12]:


# Works for either number
3/2.0


# We could also "cast" the type using a function that basically turns integers into floats. This function, unsurprisingly, is called float().

# In[14]:


# We can use this float() function to cast integers as floats:
float(3)/2


# We will go over functions in much more detail later on in this course, so don't worry if you are confused by the syntax here. Consider this a sneak preview.
# 
# One more "sneak preview" we can use to deal with classic division in Python 2 is importing from a module called __future__.
# 
# This is a module in Python 2 that has Python 3 functions, this basically allows you to import Python 3 functions into Python 2. We will go over imports and modules later in the course, so don't worry about fully understanding the import statement right now!

# In[15]:


from __future__ import division
3/2


# When you import division from the __future__ you won't need to worry about classic division occurring anymore anywhere in your code!

# ### Arithmetic continued

# In[16]:


# Powers
2**3


# In[17]:


# Can also do roots this way
4**0.5


# In[18]:


# Order of Operations followed in Python
2 + 10 * 10 + 3


# In[19]:


# Can use parenthesis to specify orders
(2+10) * (10+3)


# ## Variable Assignments
# 
# Now that we've seen how to use numbers in Python as a calculator let's see how we can assign names and create variables.
# 
# We use a single equals sign to assign labels to variables. Let's see a few examples of how we can do this.

# In[37]:


# Let's create an object called "a" and assign it the number 5
a = 5


# Now if I call *a* in my Python script, Python will treat it as the number 5.

# In[38]:


# Adding the objects
a+a


# What happens on reassignment? Will Python let us write it over?

# In[39]:


# Reassignment
a = 10


# In[40]:


# Check
a


# Yes! Python allows you to write over assigned variable names. We can also use the variables themselves when doing the reassignment. Here is an example of what I mean:

# In[41]:


# Check
a


# In[42]:


# Use A to redefine A
a = a + a


# In[43]:


# Check 
a


# The names you use when creating these labels need to follow a few rules:
# 
#     1. Names can not start with a number.
#     2. There can be no spaces in the name, use _ instead.
#     3. Can't use any of these symbols :'",<>/?|\()!@#$%^&*~-+
#     3. It's considered best practice (PEP8) that the names are lowercase.
# 
# Using variable names can be a very useful way to keep track of different variables in Python. For example:

# In[44]:


# Use object names to keep better track of what's going on in your code!
my_income = 100

tax_rate = 0.1

my_taxes = my_income*tax_rate


# In[46]:


# Show my taxes!
my_taxes


# So what have we learned? We learned some of the basics of numbers in Python. We also learned how to do arithmetic and use Python as a basic calculator. We then wrapped it up with learning about Variable Assignment in Python.
# 
# Up next we'll learn about Strings!