# 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:

Examples Number "Type"
1,2,-5,1000 Integers
1.2,-0.5,2e2,3E2 Floating-point numbers

### Basic Arithmetic

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In :

2+1

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Out:

3

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In :

# Subtraction
2-1

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Out:

1

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In :

# Multiplication
2*2

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Out:

4

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In :

# Division
3/2

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Out:

1

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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:

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In :

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

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Out:

1.5

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In :

# Works for either number
3/2.0

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Out:

1.5

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

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In :

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

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Out:

1.5

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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!

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In :

from __future__ import division
3/2

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Out:

1.5

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

### Arithmetic continued

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In :

# Powers
2**3

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Out:

8

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In :

# Can also do roots this way
4**0.5

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Out:

2.0

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In :

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

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Out:

105

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In :

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

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Out:

156

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## 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.

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In :

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

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

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In :

a+a

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Out:

10

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

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In :

# Reassignment
a = 10

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In :

# Check
a

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Out:

10

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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:

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In :

# Check
a

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Out:

10

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In :

# Use A to redefine A
a = a + a

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In :

# Check
a

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Out:

20

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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:

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In :

# 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

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In :

# Show my taxes!
my_taxes

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Out:

10.0

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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!