mpl_y_scale.py

import math 

def magnitude(x):
    """Get the order 10 magnitude of a float."""
    return int(math.log10(x))

def mpl_y_scale(datamin, datamax, desired_n_steps=5, minmax_buffer=True):
    """Determine nicely spaced, nearest-decimal-rounded y-ticks, and y-axis
    limits (with optional buffer) which centrally locate a line plot in a
    Matplotlib figure axis.
    """
    diff = datamax - datamin
    mag = magnitude(diff)
    step = 10**mag
    ymin = datamin - (datamin%step)
    if minmax_buffer and math.isclose(ymin, datamin):
        ymin-=step
    ymax = datamax - (datamax%step) + step
    if minmax_buffer and math.isclose(ymax, datamax):
        ymax+=step
    n_steps = int((ymax-ymin)/step)+1
    yticks = [ymin+(i*step) for i in range(n_steps)]
    while len(yticks)> desired_n_steps:
        yticks = [s for i, s in enumerate(yticks) if i%2==0]
    new_diff = yticks[1]-yticks[0]
    while yticks[-1]<ymax:
        yticks.append(yticks[-1]+new_diff)
    while yticks[0]>ymin:
        yticks.append(yticks[0]-new_diff)
    return ymin, ymax, yticks