python matplotlib-网格线和颜色填充未对齐

我正在使用以下代码生成一种二进制heatmap:

import numpy as np
import matplotlib.colors as mlc
import matplotlib.pyplot as mlp

states = ['AAAA', 'BBBB', 'CCCC', 'DDDD']
walk = [1, 2, 3, 2, 3, 2, 3, 2, 3, 2]

states_len = len(states)
walk_len = len(walk)

img = np.zeros((states_len, walk_len), dtype=float)

for i, s in enumerate(walk):
    img[s, i] = 1.0

figure, ax = mlp.subplots()

color_map = mlc.LinearSegmentedColormap.from_list('ColorMap', [(1.000, 1.000, 1.000), (0.984, 0.501, 0.447)])
ax.imshow(img, cmap=color_map, interpolation='none')

ax.set_xlabel('Steps', fontsize=13)
ax.set_xticks(np.arange(0, walk_len, 1))
ax.set_xticks(np.arange(-0.5, walk_len, 1), minor=True)
ax.set_xticklabels(np.arange(1, walk_len + 1, 1))

ax.set_ylabel('States', fontsize=13)
ax.set_yticks(np.arange(0, states_len, 1))
ax.set_yticks(np.arange(-.5, states_len, 1), minor=True)
ax.set_yticklabels(states)

ax.grid(which='minor', color='k')

ax.set_title('Walkplot (Sequence)', fontsize=15, fontweight='bold')

它产生了奇怪的结果:

正如您可能注意到的那样,色斑看起来并没有与网格正方形对齐。最重要的是,有时网格线的尺寸不统一,有些看起来比其他的大。

我认为这一定与长宽比或图形大小有关,但我对潜在的解决方案一无所知。我如何解决这个问题?

我当前的设置:

• Python 3.6 X64
• PyTrack 2018.1