class_docstr: A ChainMap groups multiple dicts (or other mappings) together
  to create a single, updatable view.
  
  The underlying mappings are stored in a list.  That list is public and can
  be accessed / updated using the *maps* attribute.  There is no other state.
  
  Lookups search the underlying mappings successively until a key is found.
  In contrast, writes, updates, and deletions only operate on the first
  mapping.
code: def __delitem__(self, key):
      try:
          del self.maps[0][key]
      except KeyError:
          raise KeyError(
              "Key not found in the first mapping: {!r}".format(key)
          )
  
imports: import sys
label_desc: Use image node_id 15 for calling the ChainMap obj's underlying member method code with example usage: obj.__delitem__(key) without return types