Allow getting configuration from environment variables

CHANGELOG.md

@@ -1,5 +1,10 @@
 # Change Log
 
+## 1.27.1
+
+### Improvements
+- Read config files from the environment variables ([#1422](../../pull/1422))
+
 ## 1.27.0
 
 ### Features

docs/config_options.rst

@@ -43,6 +43,11 @@ As an example, configuration parameters can be set via python code like::
 
   large_image.config.setConfig('max_small_image_size', 8192)
 
+Configuration from Environment
+------------------------------
+
+All configuration parameters can be specified as environment parameters by prefixing their uppercase names with ``LARGE_IMAGE_``.  For instance, ``LARGE_IMAGE_CACHE_BACKEND=python`` specifies the cache backend.  If the values can be decoded as json, they will be parsed as such.  That is, numerical values will be parsed as numbers; to parse them as strings, surround them with double quotes.
+
 Configuration within the Girder Plugin
 --------------------------------------
 

large_image/cache_util/cache.py

@@ -1,4 +1,5 @@
 import functools
+import pickle
 import threading
 import uuid
 
@@ -92,7 +93,7 @@ def wrapper(self, *args, **kwargs):
                     return self.cache[k]
             except KeyError:
                 pass  # key not found
-            except ValueError:
+            except (ValueError, pickle.UnpicklingError):
                 # this can happen if a different version of python wrote the record
                 pass
             v = func(self, *args, **kwargs)

large_image/config.py

@@ -1,4 +1,6 @@
+import json
 import logging
+import os
 from typing import cast
 
 try:
@@ -65,6 +67,16 @@ def getConfig(key=None, default=None):
     """
     if key is None:
         return ConfigValues
+    envKey = f'LARGE_IMAGE_{key.replace(".", "_").upper()}'
+    if envKey in os.environ:
+        value = os.environ[envKey]
+        if value == '__default__':
+            return default
+        try:
+            value = json.loads(value)
+        except ValueError:
+            pass
+        return value
     return ConfigValues.get(key, default)