python-mastery/Exercises/soln8_3.md

Exercise 8.3 - Solution

# coticker.py
from structure import Structure
from validate import String, Integer, Float

class Ticker(Structure):
    name = String()
    price = Float()
    date = String()
    time = String()
    change = Float()
    open = Float()
    high = Float()
    low = Float()
    volume = Integer()

from cofollow import consumer, follow
from tableformat import create_formatter
import csv

# Coroutine that splits rows using the CSV module.  This is rather
# mind-bending due to the fact that the csv module only understands
# iteration with the for-loop.  To make it work, we wrap it around
# a generator that simply produces the last item received.

@consumer
def to_csv(target):
    def producer():
        while True:
            yield line

    reader = csv.reader(producer())
    while True:
        line = yield
        target.send(next(reader))

@consumer
def create_ticker(target):
    while True:
        row = yield
        target.send(Ticker.from_row(row))

@consumer
def negchange(target):
    while True:
        record = yield
        if record.change < 0:
            target.send(record)

@consumer
def ticker(fmt, fields):
    formatter = create_formatter(fmt)
    formatter.headings(fields)
    while True:
        rec = yield
        row = [getattr(rec, name) for name in fields]
        formatter.row(row)

if __name__ == '__main__':
    follow('Data/stocklog.csv',
           to_csv(
           create_ticker(
           negchange(
           ticker('text', ['name','price','change'])))))

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