Creating Variables
Unlike other programming languages, Python has no command for declaring a variable.
A variable is created the moment you first assign a value to it.
x = 5
y = "John"
print(x)
print(y)
Variables do not need to be declared with any particular type and can even change type after they have been set.
x = 4 # x is of type int
x = "Sally" # x is now of type str
print(x)
A variable can have a short name (like x and y) or a more descriptive name (age, carname, total_volume). Rules for Python variables:
- A variable name must start with a letter or the underscore character
- A variable name cannot start with a number
- A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ )
- Variable names are case-sensitive (age, Age and AGE are three different variables)
Specify a Variable Type
There may be times when you want to specify a type on to a variable. This can be done with casting. Python is an object-orientated language, and as such it uses classes to define data types, including its primitive types.
Casting in python is therefore done using constructor functions:
- int() - constructs an integer number from an integer literal, a float literal (by rounding down to the previous whole number), or a string literal (providing the string represents a whole number)
- float() - constructs a float number from an integer literal, a float literal or a string literal (providing the string represents a float or an integer)
- str() - constructs a string from a wide variety of data types, including strings, integer literals and float literals