Q.Program 7-7: Write a program using a user defined function calcFact() to calculate and display the factorial of a number num passed as an argument.

Pass by Object Reference — A First Look

Imagine you have a notebook with a friend's phone number written on page 5. You tear out that page and hand it to your friend. Now your friend has their own copy of the number. If they scribble a correction on their page, your notebook still shows the old number. That's pass by value — the data itself is copied.

Now imagine instead you hand your friend the entire notebook, open to page 5. They look at the same page you're looking at. If they change the number, you both see the change. That's pass by reference — the actual object is shared.

Python, Java (for objects), JavaScript (for objects), and many other languages do something in between. They hand your friend a copy of the page number, not the page itself. But that page number tells them exactly where the notebook is. So your friend can still walk to that location and change what's written there. They just can't make your notebook point to a different page.

This middle ground is pass by object reference.

The Precise Statement

Here's the key split:

• If the object is mutable (list, dict, set, custom class instances), changes made inside the function are visible outside.
• If the object is immutable (int, float, string, tuple), any "change" creates a new object — the original is untouched.

See It in Action

def change_list(lst):
    lst.append(4)          # mutates the same list object

def reassign_list(lst):
    lst = [10, 20, 30]     # creates a new list, original unaffected

my_list = [1, 2, 3]
change_list(my_list)
print(my_list)             # [1, 2, 3, 4] — changed!

reassign_list(my_list)
print(my_list)             # [1, 2, 3, 4] — unchanged!
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