Add create_custom_constraint factory method

[amontanez24]

Problem Description

As a user, it would be easier to create my own custom constraints if the only thing I had to supply was the functions for transforming and validating.

Expected behavior

• Add a factory class method called create_custom_constraint to the constraints module.
• This method should take in the following parameters:
  • is_valid_fn: required. A function with the following signature is_valid_fn(column_names, data, **kwargs). Must return a series with the rows that are valid for the constraint set to True.
  • transform_fn: optional. A function with the following signature - transform_fn(column_names, data, **kwargs)
  • reverse_transform_fn: optional. A function with the following signature - reverse_transform_fn(column_names, data, **kwargs)
• The method should return a new constraint class object (not instance) with the is_valid, transform and reverse_transform methods set to what the user provides. The is_valid must be provided, and if either of the two tranform methods are provided, then they both must be.
• Delete the current CustomConstraint class

Additional context

• Use the following prototype as inspiration:

def create_custom_constraint(transform_fn=None, reverse_transform_fn=None,
                             is_valid_fn=None):
  
  # User must provide a validity function
  if is_valid_fn is None:
    raise Exception("Missing required parameter 'is_valid'.")
  
  # Transform & reverse are optional but should be provided together or not at all
  if transform_fn is None and reverse_transform_fn is not None:
    raise Exception('No transform is given for the reverse transform.')
  
  if transform_fn is not None and reverse_transform_fn is None:
    raise Exception('No reverse transform is given for the transform.')
  
  # Create a Class that binds to the provided functions
  class CustomConstraint:

    # can keep track of class-level attributes
    TYPE='CUSTOM_CONSTRAINT' # this lets us know how to handle it

    def __init__(self, column_names, **kwargs):
      self.column_names = column_names
      self.kwargs = kwargs
    
    def transform(self, data):
      if transform_fn is None:
        raise Exception('Transform is not defined for this custom constraint.')

      result = transform_fn(self.column_names, data, **self.kwargs)

      if data.shape[0] != result.shape[0]:
        raise Exception('Transformation did not produce the same number of rows as the original')
      return result
    
    def reverse_transform(self, data):
      if reverse_transform_fn is None:
        raise Exception('Reverse transform is not defined for this custom constraint.')

      result = reverse_transform_fn(self.column_names, data, **self.kwargs)
      
      if data.shape[0] != result.shape[0]:
        raise Exception('Reverse transformation did not produce the same number of rows as the original')
      return result
    
    def is_valid(self, data):
      result = is_valid_fn(self.column_names, data, **self.kwargs)
      
      if len(result) != data.shape[0]:
        raise Exception('The validity check should produce exactly 1 True/False value for every row in the data')
      return result

  # return the class to the user 
  return CustomConstraint