I was wondering if there is any way to prevent the external modification of instance variables in a python object by requiring the use of a "setter" method. For example, if g = gene(gene_info = {'id':'gene1', 'start':1200, end':2520}), I'd like g.gene_info = {'id':'gene1', 'start':1556, 'end':2520}) as well as g['start'] = 1556 to throw an error asking to use set_geneInfo method instead. This will be particularly useful when one needs to modify a number of other attributes related to gene_info after modifying gene_info. Here's an sample code, where variable gene_loc needs to be updated each time one modifies gene_info:

class gene(object):
    def __init__(self,gene_info):
        self.set_geneInfo(gene_info)

    def set_geneInfo(self,gene_info):
        """
        gene_info has to be a dictionary
        """
        if not isinstance(gene_info,dict):
            raise TypeError('gene_info must be a dictionary')

        self.gene_info = gene_info
        self.get_gene_loc()  # Gene gene location in the genome

    def get_gene_loc(self):
        """
        NOTE: self.gene_loc (gene location) needs to get updated each time one modifies gene_info
        """
        self.gene_loc = (self.gene_info['start' , self.gene_info['end'])

if __name__ == '__main__':
        g = gene(gene_info = {'id':'gene1', 'start':1200, 'end':2520}))
    print g.gene_loc  # Show gene location
    g.gene_info = {'id':'gene1', 'start':1556, 'end':2520}) # I'd like this to throw an error asking to use set_geneInfo so that gene_loc gets updated too
    print g.gene_loc  # checks if gene_loc was updated
    g.gene_info['start'] = 1800 # I'd like this to throw an error asking to use set_geneInfo so that gene_loc gets updated too
    print g.gene_loc  # checks if gene_loc was updated.