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In this video, we will cover expressions and variables.

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Expressions describe a type of operation the computers perform.

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Expressions are operations the python performs. For example,

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basic arithmetic operations like adding multiple numbers.

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The result in this case is 160.

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We call the numbers operands, and the math symbols in this case,

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addition, are called operators.

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We can perform operations such as traction using the subtraction sign.

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In this case, the result is a negative number.

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We can perform multiplication operations using the asterisk. The result is 25.

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In this case, the operands are given by negative and asterisk.

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We can also perform division with the forward slash-

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25 / 5 is 5.0;

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25 / 6 is approximately 4.167.

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In Python 3, the version we will be using in this course, both will result in a float.

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We can use the double slash for integer division, where the result is rounded.

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Be aware, in some cases the results are not the same as regular division.

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Python follows mathematical conventions when performing mathematical expressions.

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The following operations are in a different order.

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In both cases, Python performs multiplication,

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then addition, to obtain the final result.

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There are a lot more operations you can do with Python, check the labs for

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more examples.

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We will also be covering more complex operations throughout he course.

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The expressions in the parentheses are performed first.

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We then multiply the result by 60.

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The result is 1,920.

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Now, let's look at variables.

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We can use variables to store values. In this case, we assign a value of 1 to

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the variable my_variable using the assignment operator, i.e, the equal sign.

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We can then use the value somewhere else in the code

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by typing the exact name of the variable.

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We will use a colon to denote the value of the variable.

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We can assign a new value to my_variable using the assignment operator.

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We assign a value of 10. The variable now has a value of 10.

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The old value of the variable is not important.

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We can store the results of expressions. For example, we add several values and

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assign the result to x. X now stores the result.

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We can also perform operations on x and save the result to a new variable-y.

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Y now has a value of 2.666.

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We can also perform operations on x and assign the value x.

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The variable x now has a value: 2.666.

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As before, the old value of x is not important.

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We can use the type command in variables as well.

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It's good practice to use meaningful variable names; so,

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you don't have to keep track of what the variable is doing.

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Let say, we would like to convert the number of minutes

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in the highlighted examples to number of hours in the following music data-set.

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We call the variable, that contains the total number of minutes, total_min.

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It's common to use the underscore to represent the start of a new word.

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You could also use a capital letter.

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We call the variable that contains the total number of hours, total_hour.

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We can obtain the total number of hours by dividing total_min by 60.

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The result is approximately 2.367 hours.

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If we modify the value of the first variable,

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the value of the variable will change.

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The final result values change accordingly, but

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we do not have to modify the rest of the code.

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(Music)