Centralize `user_config_dir()` decision making (#4755)

utils/general.py

     return max(last_list, key=os.path.getctime) if last_list else ''
 
 
-def user_config_dir(dir='Ultralytics'):
-    # Return path of user configuration directory (make if necessary)
-    cfg = {'Windows': 'AppData/Roaming', 'Linux': '.config', 'Darwin': 'Library/Application Support'}  # 3 config dirs
-    path = Path.home() / cfg.get(platform.system(), '')  # OS-specific config dir
-    path = (path if is_writeable(path) else Path('/tmp')) / dir  # GCP and AWS lambda fix, only /tmp is writeable
+def user_config_dir(dir='Ultralytics', env_var='YOLOV5_CONFIG_DIR'):
+    # Return path of user configuration directory. Prefer environment variable if exists. Make dir if required.
+    env = os.getenv(env_var)
+    if env:
+        path = Path(env)  # use environment variable
+    else:
+        cfg = {'Windows': 'AppData/Roaming', 'Linux': '.config', 'Darwin': 'Library/Application Support'}  # 3 OS dirs
+        path = Path.home() / cfg.get(platform.system(), '')  # OS-specific config dir
+        path = (path if is_writeable(path) else Path('/tmp')) / dir  # GCP and AWS lambda fix, only /tmp is writeable
     path.mkdir(exist_ok=True)  # make if required
     return path
 

utils/plots.py

 """
 
 import math
-import os
 from copy import copy
 from pathlib import Path
 
 from utils.metrics import fitness
 
 # Settings
-CONFIG_DIR = Path(os.getenv('YOLOV5_CONFIG_DIR') or user_config_dir())  # Ultralytics settings dir
+CONFIG_DIR = user_config_dir()  # Ultralytics settings dir
 matplotlib.rc('font', **{'size': 11})
 matplotlib.use('Agg')  # for writing to files only