Added env var querying for default and bool

buildozer/__init__.py

@@ -934,7 +934,11 @@ class Buildozer(object):
 
     def _get_config_default(self, section, token, default=None):
         # monkey-patch method for ConfigParser
+        # get an appropriate env var if it exists, else
         # get a key in a section, or the default
+        env_var = query_env(section, token)
+        if env_var is not None:
+            return env_var
         if not self.config.has_section(section):
             return default
         if not self.config.has_option(section, token):
@@ -944,6 +948,9 @@ class Buildozer(object):
     def _get_config_bool(self, section, token, default=False):
         # monkey-patch method for ConfigParser
         # get a key in a section, or the default
+        env_var = query_env_bool(section, token)
+        if env_var is not None:
+            return env_var
         if not self.config.has_section(section):
             return default
         if not self.config.has_option(section, token):
@@ -1206,3 +1213,32 @@ def run_remote():
         pass
     except BuildozerException as error:
         Buildozer().error('%s' % error)
+
+
+def query_env(section, token):
+    '''Given config section and token names, returns the environment
+    variable SECTION_TOKEN, or None if the variable does not exist.'''
+    env_var_name = ''.join([section.upper(), '_',
+                            token.upper().replace('.', '_')])
+    env_var = os.environ.get(env_var_name)
+    return env_var
+
+def query_env_bool(section, token):
+    '''Given config section and token names, uses query_env to query an
+    appropriate environment variable. If the variable exists, coerces to a
+    bool before returning.'''
+    env_var = query_env(section, token)
+    if env_var is None:
+        return env_var
+    elif env_var.tolower() in ['1', 'yes', 'true', 'on']:
+        return True
+    elif env_var.tolower() in ['0', 'no', 'false', 'off']:
+        return False
+    else:
+        env_var_name = ''.join([section.upper(), '_',
+                                token.upper().replace('.', '_')])
+        raise ValueError('Failed to parse {} as a config boolean. Should be one'
+                         'of {}'.format(env_var_name
+                                        ['1', 'yes', 'true', 'on',
+                                         '0', 'no', 'false', 'off']))
+