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:
Now let's start with some basic arithmetic.
In :# Addition 2+1
In :# Subtraction 2-1
In :# Multiplication 2*2
In :# Division 3/2
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 :# Specifying one of the numbers as a float 3.0/2
In :# 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 :# 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 :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!
In :# Powers 2**3
In :# Can also do roots this way 4**0.5
In :# Order of Operations followed in Python 2 + 10 * 10 + 3
In :# Can use parenthesis to specify orders (2+10) * (10+3)
In :# 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 :# Adding the objects a+a
What happens on reassignment? Will Python let us write it over?
In :# Reassignment a = 10
In :# 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 :# Check a
In :# Use A to redefine A a = a + a
In :# 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 :# 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 :# 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!