Python Variables
Python is a dynamically typed programming language which means there is no need to declare the data type of variable.
Table of Contents
- Declaring Variables also with different DataTypes
- Declare Variables as Constants
- Multiple Variable Assignments
- Variables Naming Convention
- Use the function type() to display variable datatype
- Concatenate or Combine Variables together
- Global Variables
- Local Variables
- Accessing both Global and Local Variables inside a Function or Class Method
- Deleting or Dumping Variables
Post Update Timeline
Updated on : 15-07-2020
Added new topics such as Constants, Variable assignment, and naming convention, global and local variables, deleting variables, etc.
Declaring Variables also with different DataTypes
To declare a variable in Python type variable followed by equal to operator or assignment operator and then the data to be stored inside the variable.
Syntax
variable_name = data
By using the above example I can declare variables with different data types such as string, integer, boolean, and float.
name = "Kunal" age = 25 is_married = False percentage_scored = 83.50
Note
It is mandatory to declare variables without assigning values to them else NameError
the exception is thrown.
name print(name) # PYTHON OUTPUT Traceback (most recent call last): File "main.py", line 1, in name NameError: name 'name' is not defined
Declare Variables as Constants
In definition and behavior constants are different from variables. As the value assigned to them remains the same throughout the program runtime.
Note
In Python, there is no such thing as constants. However, you can create a separate constants module file where you declare all the constants and import them to other python scripts as you need. A real-world example related to this is discussed below.
How to use constants in Python Programming Language
Create a my_constants.py:
PI = 3.14159265359 MAX_YEAR = 9999 MIN_YEAR = 1
Create a my_script.py:
import my_constants print(my_constants.PI) print(my_constants.MAX_YEAR) print(my_constants.MIN_YEAR) # PYTHON OUTPUT 3.14159265359 9999 1
You can also import a particular constant from my_constants.py. In my_script.py:
from my_constants import (PI, MAX_YEAR, MIN_YEAR, ) print(PI) print(MAX_YEAR) print(MIN_YEAR) # PYTHON OUTPUT 3.14159265359 9999 1
Multiple Variable Assignments
You can also assign some data to multiple variables.
foo = bar = 25 print("foo", foo) print("bar", bar) # PYTHON VARIABLES foo 25 bar 25
Also, you can assign different variables to multiple variables in a single line.
jack, john, jim = "Hi I'm Jack", "Hi I'm John", "Hi I'm Jim" print(jack) print(john) print(jim) # PYTHON OUTPUT Hi I'm Jack Hi I'm John Hi I'm Jim
Variables Naming Convention
Variable naming convention in Python is as given below:
- Variables must start with alphabet letters which may be the upper or lower case such as Interest, PrincipalAmount, marksScored, total_marks
- Special characters are not allowed. However, you can use underscore to concatenate two words.
- Using other special characters and numbers is prohibited.
- The variable name must be readable and meaningful.
Use the function type() to display variable datatype
x = 15 #<class 'int'> interger y = "Hello Python" #<class 'str'> string z = 21.20 #<class 'float'> float a = True #<class 'bool'> boolean #print all Variables print(x, y, z, a) #print datatype of Variables print(type(x), type(y), type(z), type(a)) #python output <class 'int'> <class 'str'> <class 'float'> <class 'bool'>
Concatenate or Combine Variables together.
In Python, the variables of a different datatype can be concatenated together via symbols or operators.
Examples:
String concatenation examples.
name, age, salary = "Kapil", 25, 15000.50 print("%s whose age is %d years has take home salary %0.2f" % ( name, age, salary ) ) print("{} whose age is {} years has take home salary {}".format( name, age, salary ) ) print(f"{name} whose age is {age} years has take home salary {salary}" ) # PYTHON OUTPUT Kapil whose age is 25 years has take home salary 15000.50 Kapil whose age is 25 years has take home salary 15000.5 Kapil whose age is 25 years has take home salary 15000.5
To learn more on string concatenation visit our post by clicking here
Operations on numbers:
a = 10+5 b = 10/2 c = 5*3 d = 10%6 print(a, b, c, d) #python output 15 5.0 15 4
Global Variables
In simple definition, Global Variables are those whose value can be accessed by the other functions and classes. In most cases, variables which are global are used for the purpose of using their value throughout the program.
Declaring Global Variables in Python
name = "Jake" def print_name(): print(f"My Name is {name}") print_name() # PYTHON OUTPUT My Name is Jake
Here the variable name
is global and can be accessed inside the function print_name
.
Local Variables
Local variables are available at the function or method level scope and like global variables, local variables cannot be accessed outside the function or method.
def print_name(): name = "Jake" # This is local variable print(f"My Name is {name}") print_name() # PYTHON OUTPUT My Name is Jake
Accessing local variables outside of its scope will throw NameError exception.
def set_name(): name = "John" set_name() print(f"My Name is {name}") # PYTHON ERROR Traceback (most recent call last): File "main.py", line 6, in print(f"My Name is {name}") NameError: name 'name' is not defined
Accessing both Global and Local Variables inside a Function or Class Method
Consider a situation where you have given the same name to your global, local variable and you have to access those values based on their scopes.
Examples:
name = "kunal" def print_name(): global name # Here we are accessing global variable via keyword global print(f"My Name is {name}") print_name() # PYTHON OUTPUT My Name is kunal
You can also update the local variable value inside function.
name = "kunal" def print_name(): global name name = "Jake" # This will update the global value of variable name print(f"My Name is {name}") print(f"Value of variable name before calling function print_name() : {name}") print_name() print(f"Value of variable name after calling function print_name() : {name}") # PYTHON OUTPUT Value of variable name before calling function print_name() : kunal My Name is Jake Value of variable name after calling function print_name() : Jake
Note
Don’t try to directly assign value to a global variable like
global name = "Jake"
this will throw an exception SyntaxError: invalid syntax
.
Using global variables inside class methods.
name = "kunal" class Person: def show_name(self): global name print(f"My name is {name}") p = Person() p.show_name() # PYTHON OUTPUT My name is kunal
Deleting or Dumping Variables
You can delete or dump unused variables using del
keyword followed by a variable to dump.
Examples:
name = "kunal" del name print(name) # PYTHON OUTPUT Traceback (most recent call last): File "main.py", line 3, in print(name) NameError: name 'name' is not defined
The exception is thrown because the variable is no longer accessible after deletion. You can also add multiple variables followed by a comma to delete them.
name = "kunal" age = 12 del name, age
Note
To learn more on python variables go Visit Python.org
I have also found a great post on this topic in Programiz website.




