In this tutorial, you will learn about Python Constants. A constant is a kind of variable that has unchangeable values during execution time. In fact, constants in Python are rarely used. Typically, constants are established and assigned to a unique module or file.
Furthermore, constants have two parts, namely a name and a value. The name will give a clear idea of what the constant is, while the value will give an idea of what the constant looks like in real life.
What is a Constants in python?
In Python, Constant is a type of variable that cannot change its value, for instance constant can be thought as a simple container that holds information that cannot be changed or altered.
In addition, you can think of constants as a bag where you can put books that can’t be taken out again.
Assigning value to Python constant
In Python, assigning a value that supports constants are usually declared and assigned in a module. The module is a new file with variables and functions which is imported into the main file.
Inside the module, constants are written with all capital letters and underscores to separate the words.
For a better understanding of this kind of topic, I will give some examples below.
Also read: Const In Python In Simple Words
Example program for declaring and assigning constant
First is to create constant.py. Inside of the file declared two variables with assigning values.
For example:
HEAT = 26.2
PI = 3.14
The second thing to do is create a constant object and name it a main.py file. You must import the constant library, then call the two variables in the constant.py file.
For example:
import constant
print(constant.HEAT)
print(constant.PI)
Output:
26.2
3.14
Basic rules for naming conventions for variables and constants in Python
Names for Python constants and variables should be a mix of lowercase (a-z) or uppercase (A-Z) letters, numbers (0-9) or an underscore (_).
For example:
phoneNumber
email_add
NAME
READ_ONLY
For naming convention, you should have to create a name which is unique and related to the data you are assigning.
For example:
Number is more readable and makes more sense than declaring only a (N).
If you want to have two or more words in a variable name, you should put an underscore between them or use a camel case naming convention.
For example:
//underscore
email_add
//camel case naming convention
phoneNumber
If ever, use capital letters to declare a constant for easy identification.
For example:
HEIGHT
WEIGHT
GENDER
NATIONALITY
RELIGION
STATUS
Don’t use special symbols which is hard to familiarize.
For example:
@, !, %, *, #, $, etc.
Finally, don’t make a variable name that starts with a number.
For example:
123number
Global constants in Python
In Python, a global variable is often set at the beginning of the program. In other words, Python variables that are declared outside of a function are called “global variables.”
In addition, a global constant is a literal value that has a name given to it. Like a global variable, you can get the value of a global constant from any script or 4GL procedure in the application to get the object attribute.
For example:
g = 0 # global variable
def add():
global g
g = g + 5 # increment by 2
print("Inside add():", g)
add()
print("In main:", g)
Output:
Inside add(): 5
In main: 5
Deleting variables
In Python, deleting a variable name is easy to get rid of a variable that is not used. To free up space, we can delete any specific variable by typing del “variable name.”
For example:
g = 26
print (g)
del g
print (g)
Concatenating variables
Concatenating variables in Python programming language with different data types is easy. Like a number variable and a Python String variable, we will have to declare the number variable as a string.
Then Python will throw a TypeError if the number variable is not declared as a string variable before it is added to a string variable.
For example:
g = ‘Glenn’
l = 26
print g+l
Another example below will throw a TypeError due to variable g being a string type while variable l is an int type.
To remove this kind of error message, we need to declare the int variable as a string.
For example:
g = ‘Glenn’
l = 26
print(g + str(l))
Output:
Glenn26
Conclusion
I hope this lesson has helped you learn a lot. Check out my previous and latest articles for more life-changing tutorials that could help you a lot.