如何让bar_label使用新的格式，如百分比，千位分隔符等？

*自matplotlib 3.7起

fmt参数现在直接支持基于{}的格式字符串，例如：

# >= 3.7
plt.bar_label(bars, fmt='{:,.2f}')
#                       ^no f here (not an actual f-string)

*matplotlib 3.7之前

fmt参数不支持基于{}的格式字符串，因此使用labels参数。使用f字符串格式化bar容器的datavalues，并将其设置为labels，例如：

# < 3.7
plt.bar_label(bars, labels=[f'{x:,.2f}' for x in bars.datavalues])

示例如下：

*千个分隔符标签

bars = plt.bar(list('ABC'), [12344.56, 23456.78, 34567.89])
# >= v3.7
plt.bar_label(bars, fmt='${:,.2f}')

# < v3.7
plt.bar_label(bars, labels=[f'${x:,.2f}' for x in bars.datavalues])

*标签百分比

bars = plt.bar(list('ABC'), [0.123456, 0.567890, 0.789012])
# >= 3.7
plt.bar_label(bars, fmt='{:.2%}')  # >= 3.7

# < 3.7
plt.bar_label(bars, labels=[f'{x:.2%}' for x in bars.datavalues])

*堆叠百分比标签

x = list('ABC')
y = [0.7654, 0.6543, 0.5432]
fig, ax = plt.subplots()
ax.bar(x, y)
ax.bar(x, 1 - np.array(y), bottom=y)
# now 2 bar containers: white labels for blue bars, black labels for orange bars
colors = list('wk')
# >= 3.7
for bars, color in zip(ax.containers, colors):
    ax.bar_label(bars, fmt='{:.1%}', color=color, label_type='center')

# < 3.7
for bars, color in zip(ax.containers, colors):
    labels = [f'{x:.1%}' for x in bars.datavalues]
    ax.bar_label(bars, labels=labels, color=color, label_type='center')