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So far we've seen simple expressions like 100,
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"Hello world" or 3.14.
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These are all literal expressions where the value is the same as the expression itself.
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But expressions are like building blocks that can be
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combined to form larger and more complicated expressions.
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Operators are one way to combine expressions.
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The first operator that we'll learn is the addition operator.
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In order to use it, we write something like print out 100 plus 200.
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When I run this code note that I get the value 300.
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So, when we execute a print statement then rather than printing out the expression
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itself the expression here being 100 plus
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200 then we print out the value of that expression.
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So, this expression has
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a value of 300.
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Now, this expression uses the addition operator.
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The addition operator which is done using the plus sign expects one expression to
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the left and one expression to the right.
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What it does is it computes the value of the expression to
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the left and the value of the expression to the right.
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It adds up these two values,
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and then the value of this overall expression
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is the value of this expression plus the value of this expression.
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So, in the case of 100 plus 200,
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we add the value 100 plus the value 200,
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and the value of this overall expression ends up being 300.
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Remember that whenever we call print,
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we print out the value,
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not the expression itself,
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and so 300 gets printed in our output.
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Beyond the addition operator,
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python includes many other kinds of operators.
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So, there's subtraction.
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So, when I print out the value of five minus two then we get three.
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If we reset our code here there's also multiplication.
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Multiplication is done using the star symbol.
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So, when we print out the value of the expression two times four then we get eight.
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There's also division.
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So, when I print out ten divided by three,
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so division is done using the slash symbol.
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When I print out the value of this expression then it's ten
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divided by three which is 3.3 repeating.
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In addition to addition, multiplication, division,
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and subtraction, Python include some other kinds of operators.
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So, you'll notice here that when we take ten divided by three,
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we had two integers ten and three and we got a float as a result.
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Sometimes we don't actually want that remainder.
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So Python also includes truncated division which leaves out the remainder,
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so that we get three back,
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and it also includes the modulo operator.
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So, if I say ten and then percent sign three,
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this is the modulo operator,
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so it gives me the remainder of ten divided by three, which is one.
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Python also includes exponentiation.
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So, if I print four star star two,
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then this expression is like saying four to the power of two or four squared.
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So, the value of this expression is four squared which is 16.
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When executing code, python follows
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the normal order of operations that you might be used to in math.
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So, at highest precedence is whatever is in parentheses,
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and then below that is exponentiation.
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So, that would be something like four to the power of two.
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Below that there is multiplication, and division.
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So, that would be something like two times four,
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and then below that there is addition and
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subtraction, two plus three.
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So, what this means is that suppose that we wanted to compute
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the average of two numbers 10 and 20.
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So, if we wanted to compute the average of these two,
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which should be 15,
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then we might intuitively write something like 10 plus 20 divided by two.
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Now if I run this code,
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you'll note that I get 20.0 rather than 15,
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which is the actual average.
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The reason is that Python because division is higher in precedence than addition,
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when computing the value of this expression then Python first computes
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the value of 20 divided by two and gets 10.0.
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Then it adds 10 plus 10.0,
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and gets the value 20.0.
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If instead we wanted to first add 10 and 20,
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and then divide by two,
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then we could add parenthesis around 10 and 20.
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So, I would say print out 10 plus 20 in parentheses divided by two.
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Now what Python is going to do is it's first going to add 10 plus 20
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to get 30 and divide by two to get 15.0.
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You can see that now we're correctly getting the average of 10 and 20. See you next time.7049
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