fix: common_prefixed

dol/kv_codecs.py

@@ -417,15 +417,30 @@ def tuple_of_dict(keys):
 
 
 def _affix_encoder(string: str, prefix: str = '', suffix: str = ''):
+    """Affix a prefix and suffix to a string
+    >>> _affix_encoder('name', prefix='/folder/', suffix='.txt')
+    '/folder/name.txt'
+    """
     return f'{prefix}{string}{suffix}'
 
 
 def _affix_decoder(string: str, prefix: str = '', suffix: str = ''):
-    return string[len(prefix) : -len(suffix)]
+    """Remove prefix and suffix from string
+    >>> _affix_decoder('/folder/name.txt', prefix='/folder/', suffix='.txt')
+    'name'
+    """
+    end_idx = -len(suffix) or None  # if suffix is empty, end_idx should be None
+    return string[len(prefix) : end_idx]
 
 
 def affix_key_codec(prefix: str = '', suffix: str = ''):
-    """A factory that creates a key codec that affixes a prefix and suffix to the key"""
+    """A factory that creates a key codec that affixes a prefix and suffix to the key
+
+    >>> codec = affix_key_codec(prefix='/folder/', suffix='.txt')
+    >>> codec.encoder('name')
+    '/folder/name.txt'
+    >>> codec.decoder('/folder/name.txt')
+    """
     return KeyCodec(
         encoder=partial(_affix_encoder, prefix=prefix, suffix=suffix),
         decoder=partial(_affix_decoder, prefix=prefix, suffix=suffix),
@@ -451,7 +466,7 @@ def common_prefixed(keys: Iterable[str]):
         from dol.util import max_common_prefix
 
         prefix = max_common_prefix(keys)
-        return KeyCodecs.prefixed(prefix, simple_str_sep='')
+        return KeyCodecs.prefixed(prefix)
 
 
 def common_prefix_keys_wrap(s: Mapping):
@@ -549,7 +564,9 @@ def key_based(
         value codec to use."""
 
     def extension_based(
-        ext_mapping: dict = dflt_ext_mapping, *, default: Optional[Callable] = None,
+        ext_mapping: dict = dflt_ext_mapping,
+        *,
+        default: Optional[Callable] = None,
     ):
         """A factory that creates a key-value codec that uses the file extension to
         determine the value codec to use."""