@functools.wraps(f) makes decorator pickleable; works with multithreading

safe.py

def safe_func(default_value=None):
    def decorate(f):
        @functools.wraps(f)
        def wrapper(*args, **kwds):
            try:
                res = f(*args, **kwds)
            except:
                res = default_value
            return res
        return wrapper
    return decorate
    

@safe_func(default_value=None)
def div(x,y):
    return x / y