Operators

Let's work out how much money we make after being taxed. In a new file, tax.py, create a variable called base_salary. Assign 8000 to base_salary. Now create another variable called tax and set it to 0.15. Now that we have those two variables, let's find out how much money we actually get to keep, create one more variable as follows:

income_after_tax = base_salary * (1 - tax)
print(income_after_tax)

Congratulations! You've been the employee of the month, and the company wants to reward you with a bonus. The bonus policy states that you get twice your income after tax. Create a variable monthly_earnings with this value. Because you worked overtime, you're also going to get $200 extra. We can do that like this:

monthly_earnings = monthly_earnings + 200
print(monthly_earnings)

You should have received 13800.0.

Now let's try the same with strings. Create a variable called hello and set it to 'Hello'. Also create a variable called world and assign 'World' to it. Then write the follow:

print(hello + ' ' + world)

This is called string concatenation, simply joining strings together. What happens if we type hello - world instead?

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for -: 'str' and 'str'

The last line tells us the problem: the minus operator does not support having two strings as its arguments. Operators are available to variables depending on their types. We see that in Python the plus operator is defined for numbers and for strings but behave differently. Keep this in mind as you code, and keep reading errors as they come up.