''' Show a problem in minorticks when zooming out with toolbar.
    The problem apears when setting major ticks after a large zoomout with toolbar, but it is caused by minor ticks.
    The problem is hard to catch if you don't now this.'''

# "Locator attempting to generate 50003 ticks ([-0.2, ..., 10000.2]), which exceeds Locator.MAXTICKS (1000)."

import  matplotlib.pyplot   as      plt
from    matplotlib          import  ticker
from    matplotlib.ticker   import  MultipleLocator
from    time                import  time


class Layout:
     
    def __init__(self):
        ''' Usage of toolbar homebutton may cause the message

        "Locator attempting to generate 50003 ticks ([-0.2, ..., 10000.2]), which exceeds Locator.MAXTICKS (1000)." and

        generate thousand of objects (I assume minor ticks), needing a lot of time.
        '''

        
        fig, ax1   = plt.subplots()
        ax1.set_title('Zoom in with Toolbar to about 4990...5010. Then use home-button.', color='red')
        ax1.set( xlabel='Pointnr.', ylabel='Measure(x)', xlim=(0,10000), ylim=(-1,1) )          # No data today. Normally 30000 points with need of zooming
        ax1.grid( axis='both')
        self.fontsize = 12
         
        ax1.callbacks.connect('xlim_changed', self._ax_scaled)
        self._ax_scaled(ax1)          


    def _ax_scaled(self, ax):
        ''' Eventhandler to adopt ticks when zooming in and out.'''

        start=time()

        # ax.xaxis.set_minor_locator(MultipleLocator(10000))            # workaround with long minorticks. Use later when you have seen the problem.

        xs, xe          = ax.get_xlim()                                 # Lenght of xaxis
        majortick       = int((xe-xs)/10)

        print(f'\nSetting majortick fontsize: {majortick=} {self.fontsize=}')
        if self.fontsize==8 and majortick > 995:
            print('\nAt this point, what is the need to generate the minorticks for the whole xaxis ?')
            print('Why can´t we generate the minorticks later ?')
        self.fontsize = 12 if majortick > 7 else 8
        for ticklbl in ax.get_xticklabels():                            # set fontsize of major tick labels according to zoom
            ticklbl.set(fontsize = self.fontsize)
        print('Fontsize finished\n')

        ax.xaxis.set_minor_locator(MultipleLocator(majortick/10))       # set minor ticks to tenth of major ticks

        print(f'{time()-start=:4.1f}')                                  # Homebutton zoom out may need several minutes, be patient


f = Layout()
plt.show()