Time to refactor

After a while, we might end up with a pretty good suite of characterization tests for the legacy code. We can now approach this code like any other well-tested code and start applying the bigger refactorings with an aim to improve the design before adding our new features.

For example, we might decide to extract the print_action method into a separate Action class, or the parse_file method into a Reader class.

The following is a FileReader class where we have moved the contents from the parse_file local method:

class FileReader:
    def __init__(self, filename):
        self.filename = filename

    def get_updates(self):
        updates = []
        with open("updates.csv", "r") as fp:
            for line in fp.readlines():
                symbol, timestamp, price = line.split(",")
                updates.append((symbol, datetime.strptime(timestamp, "%Y-%m-%dT%H:%M:%S.%f"), int(price)))
        return updates

We then use the Inject Dependencies pattern to pass the reader as...