Remember
Uppercase names express an intention to keep a value unchanged. Python still permits reassignment; the convention is for people reading the code.
Python Constants
Let’s look at constants
Notice
Uppercase names express an intention to keep a value unchanged. Python still permits reassignment; the convention is for people reading the code.
Try
Follow the example, change its sample, and compare what happens.
Check
Explain the result and test your understanding.
Watch how it works
Focus on how the names, objects, and calculations change. We’ll inspect the printed output in the next section.
Explore the idea
Follow the code and watch its state change. Guided simulation.
Code
PythonDAYS_IN_WEEK = 7
weeks = 3
days = weeks * DAYS_IN_WEEK
print(days)Live state
Top-level scope
DAYS_IN_WEEK→Object 1
weeks→Object 2
days→Object 3
Object 1 · int
7Object 2 · int3Object 3 · int21This step
Uppercase names express an intention to keep a value unchanged. Python still permits reassignment; the convention is for people reading the code.
Terminal
Output(no output)
What do you expect this program to print?
Picture constants
EXAMPLE INSTRUCTIONS
DAYS_IN_WEEK = 7
weeks = 3
days = weeks * DAYS_IN_WEEK
print(days)
|
v
DISPLAYED RESULT
21
FINAL BINDINGS
DAYS_IN_WEEK --> object 1 (int)
weeks --> object 2 (int)
days --> object 3 (int)
object 1: 7
object 2: 3
object 3: 21Image brief
- Alt text
- A diagram for Python Constants. Instructions: DAYS_IN_WEEK = 7 weeks = 3 days = weeks * DAYS_IN_WEEK print(days). Displayed result: 21. The final example bindings are DAYS_IN_WEEK --> object 1 (int); weeks --> object 2 (int); days --> object 3 (int). object 1: 7; object 2: 3; object 3: 21
- Image generation prompt
- Create a clean educational illustration for a Python programming lesson titled "Python Constants". Teaching focus: Uppercase names express an intention to keep a value unchanged. Python still permits reassignment; the convention is for people reading the code. Depict exactly the relationships and labels in this reference diagram: EXAMPLE INSTRUCTIONS DAYS_IN_WEEK = 7 weeks = 3 days = weeks * DAYS_IN_WEEK print(days) | v DISPLAYED RESULT 21 FINAL BINDINGS DAYS_IN_WEEK --> object 1 (int) weeks --> object 2 (int) days --> object 3 (int) object 1: 7 object 2: 3 object 3: 21 Use a flat vector style, generous spacing, clear arrows and legible labels, with a restrained blue/teal palette on a plain background. The diagram must explain the programming idea accurately. Do not depict variables as boxes containing copied objects when they share a reference. Avoid mascots, decorative screenshots, logos, gradients and extra text. Landscape composition, approximately 3:2, suitable for a course card. Accessible description: A diagram for Python Constants. Instructions: DAYS_IN_WEEK = 7 weeks = 3 days = weeks * DAYS_IN_WEEK print(days). Displayed result: 21. The final example bindings are DAYS_IN_WEEK --> object 1 (int); weeks --> object 2 (int); days --> object 3 (int). object 1: 7; object 2: 3; object 3: 21
Follow the execution
Choose a different sample input, then follow every step through to the output. Before revealing it, predict what the program will display.
Execution workspace
Choose a sample and follow its execution. Guided simulation.
Code
PythonDAYS_IN_WEEK = 7
weeks = 3
days = weeks * DAYS_IN_WEEK
print(days)Live state
Top-level scope
DAYS_IN_WEEK→Object 1
weeks→Object 2
days→Object 3
Object 1 · int
7Object 2 · int3Object 3 · int21This step
The example has finished. Compare the final output with the values and references above.
Terminal
Output21
What do you expect this program to print?
What does this example display?
DAYS_IN_WEEK = 7
weeks = 3
days = weeks * DAYS_IN_WEEK
print(days)Which explanation matches what you learned?
Constants
In Python, a constant is a value that should not change once it's been given. For example, if you have a value like the number of days in a week, it always stays the same: 7.
While Python doesn't have a special way to make real constants (like some other languages do), we can still follow a naming rule to show that something is meant to stay the same.
How to Create a Constant in Python
We usually use capital letters for constant names, like this:
DAYS_IN_WEEK = 7
PI = 3.14
APP_NAME = "MyFirstApp"These names follow the constant naming convention. The capital letters tell us, “Hey! Don’t change this value.”
{
"array": ["7", "3.14", "MyFirstApp"],
"showIndices": false,
"highlightIndicesBlue": [0],
"highlightIndices": [1],
"highlightIndicesGreen": [2],
"labels": { "0": "DAYS_IN_WEEK", "1": "PI", "2": "APP_NAME" }
}
Using Constants
DAYS_IN_WEEK = 7
print("There are", DAYS_IN_WEEK, "days in a week.")There are 7 days in a week.Explanation: We created a constant DAYS_IN_WEEK and printed its value along with some text. The value 7 was shown because that’s what we stored in it.
What Happens If We Change a Constant?
PI = 3.14
print("Original PI:", PI)
PI = 3.14159 # changing the value
print("Changed PI:", PI)Original PI: 3.14
Changed PI: 3.14159Explanation: Python let us change the value, even though we wrote it as a constant. But this is not a good habit. Constants are called that because we should not change them.
So, it's our responsibility as programmers to treat them like fixed values and not update them later.
Tips for Using Constants
- Use capital letters with underscores:
MAX_SPEED,API_KEY,PI - Put constants at the top of your Python file so they are easy to find
- Don’t change their values once they’re set
Conclusion
Constants are values that we decide should not change. Python doesn’t force them to stay constant, but we follow rules to treat them that way.
What to remember
Connect what you noticed in the example with the idea below.
Watch out for this idea
Uppercase names cannot be reassigned by Python.
This is the misconception to avoid.Reaching the recap and completing the quizzes are separate milestones.