CODEWITHSUNDEEP
pythonpython-2.7generatoryield
BBedit
BBedit

Reputation: 8067

How to print generator object yielded value?

I'm trying to make a class I created into an infinite series generator.

The class is basically like this (I omitted the other methods as it is large):

class Step(object):
    ''' A Step taken through a field. '''
    def __init__(self, step_id, offset, danger,
        danger_limit=None, is_encounter = None, input=None):
        self.step_id = step_id
        self.offset = offset
        self.danger = danger
        self.is_encounter = is_encounter
        self.rnd = self.get_rnd(self.step_id, self.offset)
        self.danger_limit = self.get_danger_limit(self.rnd)

    def __repr__(self):
        return '{0}\t{1}\t{2}\t{3}\t{4}\t{5}\t{6}'.format(
            self.step_id, self.offset, self.danger,
            self.rnd, self.danger_limit, self.is_encounter, self.input)

    def __iter__(self):
        return self

    def advance_step(self, danger_inc=113):
        ''' To help with generator functions. '''
        # Advances the current step, so make a current step object.
        old_Step = Step(step_id=self.step_id, offset=self.offset, danger=self.danger)

        step_id = Step.get_step_id(old_Step.step_id)
        offset = Step.get_offset(step_id, old_Step.offset)
        danger = Step.get_danger(danger_inc, old_Step.danger, old_Step.danger_limit)
        new_step = Step(step_id = step_id, offset = offset, danger = danger)
        new_step.is_encounter = Step.is_encounter(new_step.danger,
            new_step.danger_limit)
        return new_step

    def next(self):
        ''' Yields next step in sequence. '''
        while True:
            yield self.advance_step()

I want to print a sequence of step objects. So I tried this:

def main():
    step = Step(step_id=250, offset=13, danger=0)
    print step.next()
    # Generate next 4 steps in sequence.
    for i in xrange(4):
        print step.next()

However, I get this output:

<generator object next at 0x104364cd0>
<generator object next at 0x104364cd0>
<generator object next at 0x104364cd0>
<generator object next at 0x104364cd0>
<generator object next at 0x104364cd0>

Expected output should look like a sequence of Step objects:

0   250 13  2048    0   74  19200   False   None
1   252 13  2048    2048    216 55552   False   None
2   254 13  2048    4096    163 41984   False   None
3   0   26  2048    6144    151 38912   False   None
4   2   26  2048    8192    212 54528   False   None

I get the expected output if I do the following:

step2 = step.advance_step()
step3 = step2.advance_step()
step4 = step3.advance_step()
print step,'\n', step2,'\n', step3,'\n', step4

How can I print the yielded step objects and not get the generator object back?

I suppose I'm doing something very wrong, but I cannot see what it is.

Upvotes: 2

Views: 1948

Answers (1)

Martijn Pieters
Martijn Pieters

Reputation: 1125068

A next() method must return one value in the sequence the iterable represents. You returned a generator for each step.

Simply return the next value, there is no need to use a loop here:

def next(self):
    ''' Yields next step in sequence. '''
    return self.advance_step()

You could just rename advance_step() to next() of course.

From the iterator.next() documentation:

Return the next item from the container. If there are no further items, raise the StopIteration exception.

Upvotes: 2

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