Magento Product Attribute Get Value

Try hasattr():

if hasattr(a, 'property'):
    a.property

See zweiterlinde's answer below, who offers good advice about asking forgiveness! A very pythonic approach!

The general practice in python is that, if the property is likely to be there most of the time, simply call it and either let the exception propagate, or trap it with a try/except block. This will likely be faster than hasattr. If the property is likely to not be there most of the time, or you're not sure, using hasattr will probably be faster than repeatedly falling into an exception block.

if ($('#A').attr('myattr')) {
    // attribute exists
} else {
    // attribute does not exist
}

EDIT:

The above will fall into the else-branch when myattr exists but is an empty string or "0". If that's a problem you should explicitly test on undefined:

if ($('#A').attr('myattr') !== undefined) {
    // attribute exists
} else {
    // attribute does not exist
}