Why was p[:] designed to work differently in these two situations?

Question

p = [1,2,3]
print(p) # [1, 2, 3]

q=p[:]  # supposed to do a shallow copy
q[0]=11
print(q) #[11, 2, 3] 
print(p) #[1, 2, 3] 
# above confirms that q is not p, and is a d         


        

Answer 1

I'm not sure if you want this sort of answer. In words, for p[:], it means to "iterate through all elements of p". If you use it in

q=p[:]

Then it can be read as "iterate with all elements of p and set it to q". On the other hand, using

q=p

Just means, "assign the address of p to q" or "make q a pointer to p" which is confusing if you came from other languages that handles pointers individually.

Therefore, using it in del, like

del p[:]

Just means "delete all elements of p".

Hope this helps.