place_inset_ax_in_data_coordinates.py

from mpl_toolkits.axes_grid.inset_locator import inset_axes

def place_inset_ax_in_data_coordinates(ax, bbox):
    """Return an ax inset in the given ax at the given bbox in
    data coordinates (bottom, left, width, height)"""
    bottom, left, width, height = bbox
    pixels_data_00 = ax.transData.transform([0,0])
    pixels_data_11 = ax.transData.transform([1,1])
    iwidth, iheight = (pixels_data_11 - pixels_data_00) / ax.figure.dpi
    return inset_locator.inset_axes(
        ax, iwidth, iheight,
        loc=10, # means "center"
        bbox_to_anchor=[bottom, left, width, height],
        bbox_transform= ax.transData
    )

def draw_curve_on_ax(ax):
    #ax.axis("off")
    ax.plot([0,1,2,3],[0,3,1,2],c="k")

import matplotlib.pyplot as plt
fig, ax = plt.subplots(1, figsize=(6,6))
draw_curve_on_ax(ax)
axc = place_inset_ax_in_data_coordinates(ax, [0.5, 0.5,1,1])
draw_curve_on_ax(axc)