[Config] Support listing sections (#217)

knack/config.py

@@ -97,6 +97,16 @@ def get(self, section, option, fallback=_UNSET):
             raise last_ex  # pylint:disable=raising-bad-type
         return fallback
 
+    def sections(self):
+        combined_sections = []
+        # Go through the config chain and combine all sections
+        for config in self._config_file_chain if self.use_local_config else self._config_file_chain[-1:]:
+            sections = config.sections()
+            for section in sections:
+                if section not in combined_sections:
+                    combined_sections.append(section)
+        return combined_sections
+
     def items(self, section):
         import re
         pattern = self.env_var_name(section, '.+')
@@ -174,6 +184,9 @@ def __init__(self, config_dir, config_path, config_comment=None):
     def items(self, section):
         return self.config_parser.items(section) if self.config_parser else []
 
+    def sections(self):
+        return self.config_parser.sections() if self.config_parser else []
+
     def has_option(self, section, option):
         return self.config_parser.has_option(section, option) if self.config_parser else False
 
@@ -234,6 +247,3 @@ def clear(self):
             for section in self.config_parser.sections():
                 self.config_parser.remove_section(section)
             self.set(self.config_parser)
-
-    def sections(self):
-        return self.config_parser.sections()