def help(self,letter='az',typ='mt'):
        """ generic help

        Parameters
        ----------

        txt : string
            'mb' | 'mt'

            mb :members
            mt :methods

        """

        members = [ x for x in self.__dict__.keys() if x not in dict.__dict__ ]
        lmeth = [ x for x in np.sort(dir(self)) if x not in dict.__dict__]

        if typ=='mb':
            print(np.sort(self.__dict__.keys()))
        if typ=='mt':
            for s in lmeth:
                if s not in members:
                    if s[0]!='_':
                        if len(letter)>1:
                            if (s[0]>=letter[0])&(s[0]<letter[1]):
                                try:
                                    doc = eval('self.'+s+'.__doc__').split('\n')
                                    print(s+': '+ doc[0])
                                except:
                                    pass
                        else:
                            if (s[0]==letter[0]):
                                try:
                                    doc = eval('self.'+s+'.__doc__').split('\n')
                                    print(s+': '+ doc[0])
                                except:
                                    pass