Python Variables

1 - Creating a variable in Python

Unlike other programming languages, Python does not have a command to declare a variable. A variable is created when you assign a value to it.

 Example

x = 7
y = "Albert"
print (x)
print (y)

Variables do not have to be declared with a particular type and can even change type after being defined.

 Example

x = 3
print (type (x)) # x is of type int
x = "Hello"
print (type (x)) # x is now of type string

2 - Variable names 

 A variable can have a short name (like x and y) or a name composed of several descriptive (age, weight, job).

3 - Rules for Python variables

• A variable name must begin with a letter or underscore 
• A variable name can not start with a number 
• A variable name can contain only alphanumeric characters and underscores (A-z, 0-9 and _) 
• A Variable names are case-sensitive (alberto, Alberto, ALBERTO are three different variables) 
• Remember that variables are case-sensitive 

4 - Output of a Variable 

The Python print() statement is often used to generate the output of variables. To combine text and a variable, Python uses the '+' character:

 Example

s = "the best programming language"
print ("Python is" + s)

You can also use the '+' character to add a variable to another variable:

 Example

x = "python is"
y = "object oriented"
z = x + y
print (z)

For numbers, the '+' character works as a mathematical operator:

 Example

x = 7
y = 2
print (x + y) # displays 9

If you try to combine a string and a number, Python will give you an error:

 Example

x = 3
y = "Alberto"
print (x + y) # Generates an error message indicating that it is not possible to add a string to a number!