Python class call a method from a class object

Question

How can I fix attribute error in this situation? I have a pandas dataframe where I make some data slicing and transformation and I want to plot the results of the persistence_model function like below.

Edit: I want to customize a function with specific title of the plot, y and x axis and create a horizontal line on the same plot from the results of persitence_model function.

class ResidualErrors():
 def __init__(self, data: pd.Series):
 self.data = data
 def _persistence_forecast_model_nrows(self, test_rows):
 slicer = test_rows + 1
 errors = self.data[-slicer:].diff().dropna()
 return errors
 def _persistence_forecast_model_percrows(self, train_perc):
 n = len(self.data)
 ntrain = int(n * train_perc)
 errors = self.data[ntrain:].diff().dropna()
 return errors
 def persistence_model(self, test_rows=None, train_perc=None):
 if (not test_rows) and (not train_perc):
 raise TypeError(r"Please provide 'test_rows' or 'train_perc' arguments.")
 if test_rows and train_perc:
 raise TypeError(r"Please choose one argument either 'test_rows' or 'train_perc'.")
 if test_rows:
 return self._persistence_forecast_model_nrows(test_rows)
 else:
 return self._persistence_forecast_model_percrows(train_perc)
 @classmethod
 def plot_residuals(obj):
 obj.plot()
 plt.show()

Desired output

res = ResidualErrors(data).persistence_model(test_rows=10)
res.plot_residuals()
>> AttributeError: 'Series' object has no attribute 'plot_residuals'

• Iguananaut: What are you trying to call obj.plot() on? Do Pandas Series have a .plot() method? I'm not sure. Here your persistence_model method returns a Series, which you would then have to pass to ResidualErrors.plot_residuals.
• timgeb: persistence_model returns a Series. A series does not have a method plot_residuals.
• matt.aurelio: I want to integrate the plotting inside the class so I can customize the title, and different matplotlib parameters.
• juanpa.arrivillaga: @matt.aurelio ok, but I don't know why you expect a @classmethod to work that way. obj will be passed the class, i.e ResidualErrors. It's not clear why you expected res.plot_residuals() to work since persistence_model returns a pandas.Series object
• DarrylG: You could change class method to def plot_residuals(cls, ser): ser.plot();plt.show(). Then call with ResidualErrors.plot_residuals(res)

Answer 1

You need to be more aware of what methods return. The first step creates a ResidualErrors object:

res = ResidualErrors(data)

The second step creates a DataFrame or Series:

obj = res.persistence_model(test_rows=10)

You can call plot_residuals on res but not on obj, as you are currently doing:

res.plot_residuals(obj)