Building Robust Object-Oriented Python Applications and Libraries/

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Reading CSV Files

Reading CSV Files

Learn how to read CSV files using various methods in Python while adhering to the DRY principle.

We'll cover the following...

Using form_dict() method

We’ll provide a common template for creating objects from CSV source data. The idea is to leverage the from_dict() methods of the various classes to create the objects our application uses:

Python 3.10.4
class TrainingData:
    def __init__(self, name: str) -> None:
        self.name = name
        self.uploaded: datetime.datetime
        self.tested: datetime.datetime
        self.training: list[TrainingKnownSample] = []
        self.testing: list[TestingKnownSample] = []
        self.tuning: list[Hyperparameter] = []
        
    def load(self, raw_data_iter) -> None:
        for n, row in enumerate(raw_data_iter):
            try:
                if n % 5 == 0:
                    test = TestingKnownSample.from_dict(row)
                    self.testing.append(test)
                else:
                    train = TrainingKnownSample.from_dict(row)
                    self.training.append(train)
            except InvalidSampleError as ex:
                print(f"Row {n+1}: {ex}")
                return
        self.uploaded = datetime.datetime.now(tz = datetime.timezone.utc)

Constructing the load() method

The load() method is partitioning the samples into testing and training subsets. It expects an iterable source of dict[str, str] objects, which are produced by a csv.DictReader object.

The user experience implemented here is to report the first failure and return. This might lead to an error message like the following:

Python 3.10.4
text Row 2: invalid species in {'sepal_length': 7.9, 'sepal_width':
3.2, 'petal_length': 4.7, 'petal_width': 1.4, 'species': 'Buttercup'}

This message has all the required information, but may not be as helpful as desired. We ...