lxml for install_requires is optional

examples/bbox_detection/labelme2voc.py

@@ -7,9 +7,14 @@ import glob
 import json
 import os
 import os.path as osp
-
-import lxml.builder
-import lxml.etree
+import sys
+
+try:
+    import lxml.builder
+    import lxml.etree
+except ImportError:
+    print('Please install lxml:\n\n    pip install lxml\n')
+    sys.exit(1)
 import numpy as np
 import PIL.Image
 

setup.py

@@ -31,7 +31,6 @@ del here
 
 
 install_requires = [
-    'lxml',
     'matplotlib',
     'numpy',
     'Pillow>=2.8.0',