Constants
Part of the Logic & Flow section of Coddy's Python journey — lesson 1 of 78.
In programming, a constant is a type of variable whose value cannot be changed during the execution of a program. Constants are useful for defining values that are used multiple times throughout a program, such as mathematical constants like PI or the number of hours in a day.
In Python, there is no strict enforcement of constants like in some other languages (such as c++). However, there is a widely adopted convention to indicate that a variable should be treated as a constant. This is done by writing the variable name in all uppercase letters, often with underscores to separate words.
For example:
PI = 3.14159
HOURS_IN_A_DAY = 24
MAX_USERS = 100When you see variables named this way in Python code, it's a signal that these values should not be altered. This convention helps make the code more readable and maintainable. It's important to note that this is just a naming convention; the Python interpreter itself does not prevent you from changing the value of these variables.
Challenge
EasyCreate a Python program that calculates the area of a circle using a constant for the value of PI. Define a constant named PI and set its value to 3.14159. Then, prompt the user to enter the radius of the circle. Calculate the area of the circle using the formula (area = PI * radius**2) and print the result.
Remember to follow the naming convention for constants by using all uppercase letters for the variable PI.
Try it yourself
# Write code here
Test yourselfThis lesson includes a short quiz. Start the lesson to answer it and track your progress.
All lessons in Logic & Flow
1Variables Exploration
ConstantsMultiple Variable AssignmentsSwapping VariablesPlaceholder VariablesRound NumbersList Casting4Contact Book Application
Display MenuAdd Contact
View ContactEdit ContactDelete ContactList AllEverything Together7Sets Part 2
Mathematical Operations Part 1Mathematical Operations Part 2Recap - Treasure HuntSubsets and SupersetsIterating Over SetsRecap - Tournament Tracker2Dictionaries Part 1
What is a Dictionary?Creating a DictionaryAccessing ValuesModifying DictionariesRecap - Recipe Manager5Advanced Decision Making
Ternary OperatorMembership ChecksIdentity ChecksIndentation ErrorsRecap - Vacation Filter8Student Records Manager
Project OverviewAdd StudentAdd GradeIs EnrolledAverage GradeList by CourseTop Students11Advanced Functions
Returning Multiple ValuesLambda Functions Part 1Lambda Functions Part 2Recap Challenge - Lambda SortRecursive Functions Part 1Recursive Functions Part 2Recap - Sum Nested List14Higher-Order Functions
The Map FunctionThe Filter FunctionRecap - Email ValidatorRecap - Number Processor3Dictionaries Part 2
Dictionary MethodsNested DictionariesChecking for KeysLooping Through DictionariesRecap - Frequency Counter9Advanced Data Aggregation
Using SumFinding Minimum and MaximumSorting Data EfficientlyRecap - Dictionary Sorter