Variable and types

Variable and types are important concepts in programming. In this article, we will learn about variables and types in Python.

Data Types

In programming, data type is an important concept.

Variables can store data of different types, and different types can do different things.

Python has the following data types built-in by default, in these categories:

• Text Type: str
• Numeric Types: int, float
• Sequence Types: list, tuple
• Mapping Type: dict
• Set Types: set
• Boolean Type: bool

Setting the Data Type

In Python, the data type is set when you assign a value to a variable:

Example

x = "Hello World"   # str
x = 20  # int
x = 20.5    # float
x = ["apple", "banana", "cherry"]   # list
x = ("apple", "banana", "cherry")   # tuple
x = {"name" : "John", "age" : 36}   # dict
x = {"apple", "banana", "cherry"}   # set
x = True    # bool

Setting the Specific Data Type

If you want to specify the data type, you can use the following constructor functions:

Example

x = str("Hello World")  # str
x = int(20) # int
x = float(20.5) # float
x = list(("apple", "banana", "cherry")) # list
x = tuple(("apple", "banana", "cherry"))    # tuple
x = dict(name="John", age=36)   # dict
x = set(("apple", "banana", "cherry"))  # set

Getting the Data Type

You can get the data type of any object by using the type() function:

Example

x = 5
print(type(x))

Output

<class 'int'>

Example

x = 5
y = "John"
print(x)
print(y)

Output

5
John

Variable names

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)

We can differentiate the two as CamelCase and snake_case. CamelCase is used for class names and snake_case is used for function and variable names.

Example

myVariableName = "John"
my_variable_name = "John"

Assign Value to Multiple Variables

Python allows you to assign values to multiple variables in one line:

Example

x, y, z = "Orange", "Banana", "Cherry"
print(x)
print(y)
print(z)

Output

Orange
Banana
Cherry

And you can assign the same value to multiple variables in one line:

Example

x = y = z = "Orange"
print(x)
print(y)
print(z)

Output

Orange
Orange
Orange

Output

Variables

The Python print statement is often used to output variables.

To combine both text and a variable, Python uses the + character:

Example

x = "awesome"
print("Python is " + x)

Output

Python is awesome

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

Example

x = "Python is "
y = "awesome"
z =  x + y
print(z)

Output

Python is awesome

This is known as concatenation.

You can also use the + character for mathematical operations:

Example

x = 5
y = 10
print(x + y)

Output

15

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

Example

x = 5
y = "John"
print(x + y)

Output

TypeError: unsupported operand type(s) for +: 'int' and 'str'

Global Variables

Variables that are created outside of a function (as in all of the examples above) are known as global variables.

Global variables can be used by everyone, both inside of functions and outside.

Example

x = "awesome"

def myfunc():
  print("Python is " + x)

myfunc()

Output

Python is awesome

If you create a variable with the same name inside a function, this variable will be local, and can only be used inside the function. The global variable with the same name will remain as it was, global and with the original value.

Example

x = "awesome"

def myfunc():
  x = "fantastic"
  print("Python is " + x)

myfunc()

print("Python is " + x)

Output

Python is fantastic
Python is awesome

The global Keyword

Normally, when you create a variable inside a function, that variable is local, and can only be used inside that function.

To create a global variable inside a function, you can use the global keyword.

Example

def myfunc():
  global x
  x = "fantastic"

myfunc()

print("Python is " + x)

Output

Python is fantastic

Also, use the global keyword if you want to change a global variable inside a function.

Example

x = "awesome"

def myfunc():
  global x
  x = "fantastic"

myfunc()

print("Python is " + x)

Output

Python is fantastic