ex 8.1, 8.2, 8.3

.gitignore

@@ -159,3 +159,4 @@ cython_debug/
 #  option (not recommended) you can uncomment the following to ignore the entire idea folder.
 #.idea/
 Session.vim
+Data/stocklog.csv

cofollow.py

@@ -0,0 +1,34 @@
+import os
+import time
+from functools import wraps
+
+
+def follow(filename, target):
+    with open(filename, 'r') as f:
+        f.seek(0, os.SEEK_END)
+        while True:
+            line = f.readline()
+            if line != '':
+                target.send(line)
+            else:
+                time.sleep(0.1)
+
+
+def consumer(func):
+    @wraps(func)
+    def start(*args, **kwargs):
+        f = func(*args, **kwargs)
+        f.send(None)
+        return f
+    return start
+
+
+@consumer
+def printer():
+    while True:
+        item = yield
+        print(item)
+
+
+if __name__ == '__main__':
+    follow('Data/stocklog.csv', printer())

coticker.py

@@ -0,0 +1,57 @@
+import csv
+
+from cofollow import consumer
+from tableformat import create_formatter
+from ticker import Ticker
+
+
+@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__':
+    from cofollow import follow
+
+    follow(
+        'Data/stocklog.csv',
+        to_csv(
+            create_ticker(
+                negchange(
+                    ticker('text', ['name', 'price', 'change'])
+                )
+            )
+        )
+    )

follow.py

@@ -0,0 +1,23 @@
+import os
+import time
+
+
+def follow(filename):
+    f = open(filename)
+    f.seek(0, os.SEEK_END)
+    while True:
+        line = f.readline()
+        if line == '':
+            time.sleep(0.1)
+            continue
+        yield line
+
+
+if __name__ == '__main__':
+    for line in follow('Data/stocklog.csv'):
+        fields = line.split(',')
+        name = fields[0].strip('"')
+        price = float(fields[1])
+        change = float(fields[4])
+        if change < 0:
+            print(f"{name:s} {price:10.2f} {change:10.2f}")

structure.py

@@ -35,7 +35,7 @@ class Structure(metaclass=StructureMeta):
         validate_attributes(cls)
 
     def __repr__(self):
-        args = map(lambda field: f"{field}={getattr(self, field)!r}", self._fields)
+        args = map(lambda field: f"{getattr(self, field)!r}", self._fields)
         return f"{type(self).__name__}({', '.join(args)})"
 
     def __setattr__(self, name, value):
@@ -44,6 +44,13 @@ class Structure(metaclass=StructureMeta):
         else:
             raise AttributeError(f"No attribute {name}")
 
+    def __iter__(self):
+        for name in self._fields:
+            yield getattr(self, name)
+
+    def __eq__(self, other):
+        return isinstance(other, type(self)) and tuple(self) == tuple(other)
+
     @classmethod
     def create_init(cls):
         code = f'def __init__(self, {", ".join(cls._fields)}):\n'
@@ -53,6 +60,10 @@ class Structure(metaclass=StructureMeta):
         exec(code, locs)
         cls.__init__ = locs['__init__']
 
+    @classmethod
+    def from_row(cls, row):
+        return cls(*[func(val) for func, val in zip(cls._types, row)])
+
 
 def typed_structure(clsname, **validators):
     cls = type(clsname, (Structure,), validators)

ticker.py

@@ -0,0 +1,28 @@
+from structure import Structure
+
+
+class Ticker(Structure):
+    name = String()
+    price = Float()
+    date = String()
+    time = String()
+    change = Float()
+    open = Float()
+    high = Float()
+    low = Float()
+    volume = Integer()
+
+
+if __name__ == '__main__':
+    import csv
+
+    from follow import follow
+    from tableformat import create_formatter, print_table
+
+    formatter = create_formatter('text')
+
+    lines = follow('Data/stocklog.csv')
+    rows = csv.reader(lines)
+    records = (Ticker.from_row(row) for row in rows)
+    negative = (rec for rec in records if rec.change < 0)
+    print_table(negative, ['name', 'price', 'change'], formatter)