raise TypeError exception for incorrect input value in a class

Question

I am trying to write a class and I want that if the initial input values for the class don't obey specific types, it would raise an exception. For instance I would use except TypeError to return an error. I don't know how it should be done though. My first attempt to write the class is as following:

class calibration(object):
      def __init__(self, inputs, outputs, calibration_info, interpolations=2):
          try:
            self.inputs=inputs
          except TypeError

          self.outputs=outputs
          self.cal_info=calibration_info
          self.interpol=interpolations

I would like that if inputs value is not a string then it raises an error message. I would appreciate for any help.

Answer 1

Its a bit different between 2.x and 3.x, but use isinstance to figure out type and then raise the exception if you are not satisfied.

class calibration(object):
    def __init__(self, inputs, outputs, calibration_info, interpolations=2):
        if not isinstance(inputs, basestring):
            raise TypeError("input must be a string")

Python2 differentiates between ascii and unicode strings - "basestring" convers them both. In python3, there are only unicode strings and you use 'str' instead.