how to use var_dump and print_r in magento

This one is crazy with magento because sometimes it works and sometimes it just shows blank page. Once it gave me a real hard time. Finally found solution somewhere.

//I just had to do was add 
->debug()

//on the object that i wanted to print as:
$obj->debug();

//e.g. if i had
$_cart = Mage::getModel('checkout/cart');

//to use print_r or var_dump, i needed to do
print_r($_cart->debug());

These are methods available for a product:

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