Fix isascii() method calls for python 3.6 (ultralytics#4958)

* fix isascii for python3.6

* update comment with python 3.7 note

Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

utils/general.py

@@ -160,6 +160,11 @@ def is_pip():
     # Is file in a pip package?
     return 'site-packages' in Path(__file__).resolve().parts
 
+def is_ascii(s=''):
+    # Is string composed of all ASCII (no UTF) characters? (note str().isascii() introduced in python 3.7)
+    s = str(s)  # convert list, tuple, None, etc. to str
+    return len(s.encode().decode('ascii', 'ignore')) == len(s)
+
 
 def is_chinese(s='人工智能'):
     # Is string composed of any Chinese characters?

utils/plots.py

@@ -17,7 +17,7 @@
 import torch
 from PIL import Image, ImageDraw, ImageFont
 
-from utils.general import user_config_dir, is_chinese, xywh2xyxy, xyxy2xywh
+from utils.general import user_config_dir, is_ascii, is_chinese, xywh2xyxy, xyxy2xywh
 from utils.metrics import fitness
 
 # Settings
@@ -68,7 +68,7 @@ class Annotator:
     # YOLOv5 Annotator for train/val mosaics and jpgs and detect/hub inference annotations
     def __init__(self, im, line_width=None, font_size=None, font='Arial.ttf', pil=False, example='abc'):
         assert im.data.contiguous, 'Image not contiguous. Apply np.ascontiguousarray(im) to Annotator() input images.'
-        self.pil = pil or not example.isascii() or is_chinese(example)
+        self.pil = pil or not is_ascii(example) or is_chinese(example)
         if self.pil:  # use PIL
             self.im = im if isinstance(im, Image.Image) else Image.fromarray(im)
             self.draw = ImageDraw.Draw(self.im)
@@ -80,7 +80,7 @@ def __init__(self, im, line_width=None, font_size=None, font='Arial.ttf', pil=Fa
 
     def box_label(self, box, label='', color=(128, 128, 128), txt_color=(255, 255, 255)):
         # Add one xyxy box to image with label
-        if self.pil or not label.isascii():
+        if self.pil or not is_ascii(label):
             self.draw.rectangle(box, width=self.lw, outline=color)  # box
             if label:
                 w, h = self.font.getsize(label)  # text width, height