There is a broad and colorful history behind pronouncing non-alphabet characters on the keyboard. I won't go into that history in order to answer this question, but some searching would help you find more if you are interested.
Specifically, here are some of the most common programmer pronunciations for punctuation, starting with the specific ones asked in the question:
It gets even more interesting, as there are some common combinations of these characters found in programming history... they have sometimes taken on pronunciations of their own:
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