def apply(self, f):
        self.input = f(self.input)
        return self
Get all the header fields and values.
dataset/ETHPy150Open uwescience/raco/raco/algebra.py/UnaryOperator.apply--crossover with--dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-1.2/django/core/servers/basehttp.py/Headers.items