tsuriga · March 20, 2016 13:48 · Mar 20, 2016
diff --git a/config.ini b/config.ini
@@ -0,0 +1,26 @@
+[DEFAULT]
+; Operation mode
+; This is a global value for all sections
+mode = master
+
+[server]
+
+; Connection lifetime
+timeout = 3600
+
+; Garbage collection mode
+; Accepted values: none, aggressive, smart, auto
+gc_mode = smart
+
+; Notice there is no mode set under this section - it will be read from defaults
+
+
+[client]
+
+; Fallback procedure for clients
+; Accepted values: none, polling, auto
+; Invalid value as an example here
+fallback = socket
+
+; Overriding global value here
+mode = slave
diff --git a/validate.py b/validate.py
@@ -0,0 +1,59 @@
+from configparser import ConfigParser
+
+
+class MyException(Exception):
+    pass
+
+
+class MyConfig(ConfigParser):
+    def __init__(self, config_file):
+        super(MyConfig, self).__init__()
+
+        self.read(config_file)
+        self.validate_config()
+
+    def validate_config(self):
+        required_values = {
+            'server': {
+                'timeout': None,
+                'gc_mode': ('none', 'aggressive', 'smart', 'auto'),
+                'mode': ('master')
+            },
+            'client': {
+                'fallback': ('none', 'polling', 'auto'),
+                'mode': ('master', 'slave')
+            }
+        }
+        """
+        Notice the different mode validations for global mode setting: we can
+        enforce different value sets for different sections
+        """
+
+        for section, keys in required_values.items():
+            if section not in self:
+                raise MyException(
+                    'Missing section %s in the config file' % section)
+
+            for key, values in keys.items():
+                if key not in self[section] or self[section][key] == '':
+                    raise MyException((
+                        'Missing value for %s under section %s in ' +
+                        'the config file') % (key, section))
+
+                if values:
+                    if self[section][key] not in values:
+                        raise MyException((
+                            'Invalid value for %s under section %s in ' +
+                            'the config file') % (key, section))
+
+cfg = {}
+
+try:
+    # The example config file has an invalid value so cfg will stay empty first
+    cfg = MyConfig('config.ini')
+except MyException as e:
+    # Initially you'll see this due to the invalid value
+    print(e)
+else:
+    # Once you fix the config file you'll see this
+    print(cfg['client']['fallback'])
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