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Exercises/soln8_3.md

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+# Exercise 8.3 - Solution
+
+```python
+# 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'])))))
+```
+
+
+
+[Back](ex8_3.md)