python Elementtree 生成带缩进格式的xml文件

示例

之前拿ET写xml,直接对root节点调用write函数，会出现产生的xml字符串没有缩进，是干巴巴的一行，可读性比较差，就像下面这样：

<annotation><filename>VW_CH3ENTERPRIZEVsTaurus_BO2_1_4_7.jpg</filename><size><width>168.81600000000006</width><height>121.66920000000009</height></size><object><name>Car</name><bndbox><xmin>14.068</xmin><ymin>10.139</ymin><xmax>154.748</xmax><ymax>111.53</ymax><width>140.68000000000006</width><height>101.39100000000008</height></bndbox></object><object><name>RedArmor3</name><bndbox><xmin>71.108</xmin><ymin>68.439</ymin><xmax>116.728</xmax><ymax>93.787</ymax><width>45.61999999999989</width><height>25.347999999999956</height></bndbox></object><object><name>RedArmor3</name><bndbox><xmin>17.878</xmin><ymin>59.567</ymin><xmax>44.488</xmax><ymax>87.45</ymax><width>26.6099999999999</width><height>27.883000000000038</height></bndbox></object><object><name>RedArmor3</name><bndbox><xmin>39.418</xmin><ymin>44.359</ymin><xmax>72.368</xmax><ymax>74.776</ymax><width>32.950000000000045</width><height>30.41700000000003</height></bndbox></object></annotation>

解决办法

看到一个不错的方法：
https://www.cnblogs.com/muffled/p/3462157.html
原理 先对root进行修饰，调用一个自定义的修饰函数

def indent(elem, level=0):
    i = "\n" + level