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Variables
 

Variables play a very important role in most programming languages, and Python is no exception. A variable allows you to store a value by assigning it to a name, which can be used to refer to the value later in the program.

To assign a variable, use one equals sign. Unlike most lines of code we’ve looked at so far, it doesn’t produce any output at the Python console. 

>> x = 7
>>> print(x)
7
>>> print(x + 3)
10
>>> print(x)

 

NOTE!
You can use variables to perform corresponding operations, just as you did with numbers and strings. As you can see, the variable stores its value throughout the program.

Variables
 

Variables can be reassigned as many times as you want, in order to change their value.
In Python, variables don’t have specific types, so you can assign a string to a variable, and later assign an integer to the same variable.

>> x = 123.456
>>> print(x)
123.456
>>> x = “This is a string”
>>> print(x + “!”)
This is a string

 

NOTE!
However, it is not good practice. To avoid mistakes, try to avoid overwriting the same variable with different data types.

Variable Names
 

Certain restrictions apply in regard to the characters that may be used in Python variable names. The only characters that are allowed are letters, numbers, and underscores. Also, they can’t start with numbers.
Not following these rules results in errors.

>> this_is_a_normal_name = 7

>>> 123abc = 7
SyntaxError: invalid syntax

>>> spaces are not allowed
SyntaxError: invalid syntax 

 

NOTE!
Python is a case sensitive programming language. Thus, Lastname and lastname are two different variable names in Python.

Variables
 

Trying to reference a variable you haven’t assigned to causes an error.
You can use the del statement to remove a variable, which means the reference from the name to the value is deleted, and trying to use the variable causes an error. Deleted variables can be reassigned to later as normal.

>> foo = “a string”
>>> foo
‘a string’
>>> bar
NameError: name ‘bar’ is not defined
>>> del foo
>>> foo
NameError: name ‘foo’ is not defined 

 

You can also take the value of the variable from the user input.

>> foo = input(“Enter a number: “)
Enter a number: 7
>>> print(foo)

 

NOTE!
The variables foo and bar are called metasyntactic variables, meaning that they are used as placeholder names in example code to demonstrate something.

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