choosing a random number from a tuple + some numbers

I have a tuple of numbers, and I want to choose a random number from my tuple in addition with a certain number. For example:

my_tuple = (1,2,3)

and I have the number 4. I want to choose a random number from the numbers 1,2,3,4 (without changing the tuple of course).

I tried:

my_tp = (1, 2, 3)
a = random.choice(list(my_tp).append(4))
print(a)

I'm new to python. I tried converting the tuple to a list, and then performing the random function. The code above didn't work. Got the error

object of type 'NoneType' has no len()

Would love some help.