Finding a decent apartment in this city – or any apartment at all, for that matter – is agonizing enough. Add a pet to the equation, and even your broker will groan along with you. “When people call and say they have a dog, it’s like, ‘Oh God, no!’ ” says Janice Silver of Bellmarc Brokerage. “We have to cross off 30 percent of our list right off the bat.” If you can’t part with your beloved pooch, python, or cockatiel, Silver suggests checking out www.nycdoglife.com, a Website that posts Bellmarc’s and other brokers’ pet-friendly co-op, condo, and rental listings. Most are for the Upper East Side, the Upper West Side, and the West Village, in that order, since those neighborhoods have the highest concentration of prewar buildings, which, as Silver explains, tend to be the most welcoming to our fellow members of the animal kingdom. And for good reason: thicker walls, fewer apartments (and therefore pets), and shorter hallways in which to leave a puddle.