tutorial.rst

Tutorials

Some tutorials for using and extending Good Tables.

1. Implementing a custom processor

# TODO: This is unfinished.

Implementing a custom validator that can be invoked in a pipeline is easy.

Let's write one that checks that values are in a certain range.

For data, see the file custom-range.csv in the examples directory.

In our data, we have name, age and city data for a group of people.

We want to ensure that all the people in our data are in the 25-50 age range.

For demonstration, we'll write a pretty specific validator for this.

Of course the implementation could be made more generic for a range scenarios.

Our validator class:

class AgeRangeValidator(object):
    column_name = 'age'
    column_type = int
    column_range = (25, 50)
    report = {}

    def run_row(self, index, headers, row):
        valid = True

        return valid

    def run():
        valids = []
        return valid, report

    def generate_report():
        return report

As you can see, we hard coded column_name, column_type and column_range.

Also, we are running our validation through the run_row method, which is the most common method used for validations.

However, we could easily run the same validation in the run_column instead:

# stuff
def run_column():
valid = True
    return valid

So, let's see it in action. First, we'll run the validator in 'stand alone' via its run method:

validator = AgeRangeValidator()
filepath = 'examples/custom-range.csv'
valid, report = validator.run(filepath)

And the same, but part of a validation pipeline using the structure validator with our AgeRangeValidator:

validators = ('structure', 'my_module.AgeRangeValidator')
filepath = 'examples/custom-range.csv'
validation_pipeline = ValidationPipeline(filepath, validators)
valid, report = validation_pipeline.run()