'Sets and returns default axis object for dendrogram figure.
:param (str) axis_key: E.g., \'xaxis\', \'xaxis1\', \'yaxis\', yaxis1\', etc.
:rtype (dict): An axis_key dictionary with set parameters.'

def set_axis_layout(self, axis_key):

    axis_defaults = {'type': 'linear', 'ticks': 'outside', 'mirror': 'allticks', 'rangemode': 'tozero', 'showticklabels': True, 'zeroline': False, 'showgrid': False, 'showline': True}
    if (len(self.labels) != 0):
        axis_key_labels = self.xaxis
        if (self.orientation in ['left', 'right']):
            axis_key_labels = self.yaxis
        if (axis_key_labels not in self.layout):
            self.layout[axis_key_labels] = {}
        self.layout[axis_key_labels]['tickvals'] = [(zv * self.sign[axis_key]) for zv in self.zero_vals]
        self.layout[axis_key_labels]['ticktext'] = self.labels
        self.layout[axis_key_labels]['tickmode'] = 'array'
    self.layout[axis_key].update(axis_defaults)
    return self.layout[axis_key]
