You could also take your scuba class (course and pool work)at home, as Marty suggested; then take the open water certification portion at your destination. There are several very good dive operations in San Pedro that will provide open water certification on a referral basis. The Scuba diving classes that you take at home will take approx 4 weeks (one afternoon or evening per week) to complete. Many local dive shops, plus many YMCA's, will offer the scuba diving class. The referral certification class at your destination takes two days of two tank dives under the supervision of an instructor. (Just think of this as your first 4 scuba diving adventures.) Hustler Tours, Ramon Dive Center, and Amigo del Mar are three of the many shops in San Pedro that offer this service.
As Marty mentioned, diving safely is the most important factor; and training is the key to attaining this. So give it careful consideration, I guarantee that you will really enjoy this sport.