Command to delete inside parentheses doesn't work [duplicate]

Question

Let's say I have a line of code:

for i in range(1, 100):

My cursor is on the f in for, and I want to delete the text inside the parenthesis. In other words, I want my line to look like this:

for i in range():

Where my cursor is on the second parenthesis. My initial instinct, after reading this post, was to type di( (see "A text object reference"). However, this does nothing. I also tried dib as suggested by this post (see second answer), but again, nothing happened. What should I do to delete the text between the two parentheses?
Thanks in advance!