Statements
Contents
Statements¶
Statements are commands and can be executed. Statements are formed using assignments, sequences, conditionals, loops and methods This chapter shows you how to use statements.
The book Introduction to programming in Python presents some statements in chapter 1.3
Expressions vs statements¶
While expressions have values, statements are instructions (commands), most often to make changes in the program or to do something in the environment for the program: for example printing to standard output, or drawing to the screen or using a file.
We will start from the most elementary statement: assignment. For this we need to introduce variables. You might have noticed that the chapter on expressions did not use variables. Well, actually yes: in some list comprehensions we did! But this was very much like the use of variables in math. For assignments we need to understand variables as boxes where we can store objects. Assignment is the statement for changing the object that is stored in a box.
Variables are identifiers that you can introduce in your program as you need them: when you assign them an object for the first time. In Python assignments look as follows:
variable = expression
Now you see why we started with expressions: we need them to say what object (value) we want to store in a variable.
Note
Notice that the assignment statement has a variable to the left and an expression to the right and is not a comparison between two values.
Warning
The symbol = should not be confused with equality.
In Python equality is an operation and is designated with ==.
I tis used with two expressions as in
expression == expression