# Numbers

@mrtutor

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

```# Addition
2+1
```

```3
```

```# Subtraction
2-1
```

```1
```

```# Multiplication
2*2
```

```4
```

```# Division
3/2
```

```1
```

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:

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

```1.5
```

```# Works for either number
3/2.0
```

```1.5
```

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

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

```1.5
```

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!

```from __future__ import division
3/2
```

```1.5
```

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

### Arithmetic continued

```# Powers
2**3
```

```8
```

```# Can also do roots this way
4**0.5
```

```2.0
```

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

```105
```

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

```156
```

### 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.

```# 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.

```# Adding the objects
a+a
```

```10
```

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

```# Reassignment
a = 10
```

```# Check
a
```

```10
```

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:

```# Check
a
```

```10
```

```# Use A to redefine A
a = a + a
```

```# Check
a
```

```20
```

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:

```# 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
```

```# Show my taxes!
my_taxes
```

```10.0
```

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!