[SOLVED] Why does the Python datetime.replace() method return a new object instead of mutate the existing object?

Why does the Python datetime.replace() method return a new object instead of mutate the existing object?

Calling the .replace() method on a Python DateTime object returns a new instance of a DateTime object instead of mutating the existing object. This seems to be a common pitfall when learning the method.

Solution

datetime objects in Python are immutable - this is an intentional design choice that provides thread safety and predictable behavior. This immutable behavior is consistent with other built-in Python types like strings and tuples. It's a powerful feature that helps prevent unintended side effects in your code.

So this is a sample usage:

from datetime import datetime

# Create a datetime object
current_date = datetime(2024, 12, 12, 12, 30)

# Correct usage - assign the new value
new_date = current_date.replace(hour=15)

# Now new_date has hour=15, while current_date remains unchanged
print(new_date)        # 2024-12-12 15:30:00
print(current_date)    # 2024-12-12 12:30:00