diff --git a/src/pymusco/core.py b/src/pymusco/core.py
index c3e774a..16c5ec7 100644
--- a/src/pymusco/core.py
+++ b/src/pymusco/core.py
@@ -8,6 +8,7 @@
 import abc
 import json
 import re
+from pathlib import Path
 import PyPDF2  # sudo port install py27-pypdf2
 from PIL import Image
 
@@ -19,13 +20,13 @@ def dict_raise_on_duplicates(ordered_pairs):
     d = {}
     for k, v in ordered_pairs:
         if k in d:
-            raise ValueError(f"duplicate key: {k:%r}")
+            raise ValueError(f"duplicate key: {k!r}")
         else:
             d[k] = v
     return d
 
 
-def load_commented_json(commented_json_file_path):
+def load_commented_json(commented_json_file_path: Path):
     uncommented_json_contents = ''
     with open(commented_json_file_path, 'rt', encoding='utf-8') as file:
 
@@ -211,7 +212,7 @@ def get_instrument(self, instrument_id):
         raise InstrumentNotFound(instrument_id)
 
 
-def load_orchestra(orchestra_file_path):
+def load_orchestra(orchestra_file_path: Path):
     """
 
     Parameters
@@ -302,13 +303,13 @@ def get_id(self):
         """
         uid = self.instrument.get_id()
         if self.is_solo:
-            uid = f'{uid:%s} solo'
+            uid = f'{uid:s} solo'
         if self.voice is not None:
-            uid = f'{uid:%s} {self.voice:%d}'
+            uid = f'{uid:s} {self.voice:d}'
         if self.clef is not None:
-            uid = f'{uid:%s} {self.clef:%s}'
+            uid = f'{uid:s} {self.clef:s}'
         if self.is_disabled:
-            uid = f'{uid:%s} disabled'
+            uid = f'{uid:s} disabled'
         return uid
 
     def __lt__(self, other):
@@ -371,7 +372,7 @@ def __init__(self, orchestra, track_id_to_page=None):
                 self.track_to_page[track] = page
 
     def __repr__(self):
-        return "{%s}" % ', '.join([f"{str(key)}: {value:%d}" for key, value in self.track_to_page.items()])
+        return "{%s}" % ', '.join([f"{str(key)}: {value:d}" for key, value in self.track_to_page.items()])
 
     def __str__(self):
         return "[%s]" % ', '.join([f'"{str(key)}"' for key in self.track_to_page.keys()])  # pylint: disable=consider-iterating-dictionary, consider-using-f-string
diff --git a/src/pymusco/piece.py b/src/pymusco/piece.py
index 8463207..9ffd95d 100644
--- a/src/pymusco/piece.py
+++ b/src/pymusco/piece.py
@@ -6,9 +6,9 @@
 from .main import stub_to_print
 from .core import TableOfContents
 from .core import load_commented_json
+from .core import Orchestra
 from .tssingle import SingleTrackSelector
 
-
 def dict_to_toc(toc_as_dict, orchestra):
     """
     Parameters
@@ -20,7 +20,7 @@ def dict_to_toc(toc_as_dict, orchestra):
     # check that the keys used in this dictionary are known
     for key in toc_as_dict.keys():
         if key not in ['format', 'track_id_to_page']:
-            raise KeyError('unexpected key in toc dictionary : %s' % (key))
+            raise KeyError(f'unexpected key in toc dictionary : {key:s}')
 
     toc = TableOfContents(orchestra=orchestra, track_id_to_page=None)
     for track_id, page_index in toc_as_dict['track_id_to_page'].items():
@@ -44,8 +44,6 @@ def toc_to_dict(toc):
 
 
 def dict_to_stamp_desc(stamp_desc_as_dict, piece_desc_file_path):
-    """
-    """
     abs_stamp_file_path = None
     stamp_file_path = Path(stamp_desc_as_dict['stamp_image_path'])
     allowed_image_suffixes = ['.pdf', '.png']
@@ -54,9 +52,9 @@ def dict_to_stamp_desc(stamp_desc_as_dict, piece_desc_file_path):
     else:
         abs_stamp_file_path = piece_desc_file_path.parent.resolve() / stamp_file_path
     if not abs_stamp_file_path.exists():
-        raise FileNotFoundError("The stamp file '%s' is missing (file not found)." % (abs_stamp_file_path))
+        raise FileNotFoundError(f"The stamp file '{abs_stamp_file_path:s}' is missing (file not found).")
     if abs_stamp_file_path.suffix not in allowed_image_suffixes:
-        raise TypeError("Unsupported image format for stamp '%s' (allowed formats : %s) " % (abs_stamp_file_path, str(allowed_image_suffixes)))
+        raise TypeError(f"Unsupported image format for stamp '{abs_stamp_file_path}' (allowed formats : {str(allowed_image_suffixes)}) ")
     return StampDesc(file_path=abs_stamp_file_path,
                      scale=stamp_desc_as_dict['scale'],
                      tx=stamp_desc_as_dict['tx'],
@@ -107,7 +105,7 @@ def piece_to_dict(piece):
     return piece_as_dict
 
 
-def load_piece_description(piece_desc_file_path, orchestra):
+def load_piece_description(piece_desc_file_path: Path, orchestra):
     """
 
     Parameters
@@ -172,7 +170,7 @@ def __init__(self, uid, title, orchestra, scan_toc, missing_tracks=None, stamp_d
 
     @property
     def label(self):
-        return '%03d-%s' % (self.uid, self.title.replace(' ', '-'))
+        return f"{self.uid:03d}-{self.title.replace(' ', '-')}"
 
     # def get_stub_toc(self):
     #     """
@@ -248,7 +246,13 @@ def build_all(self, musician_count):
 class Catalog(object):
     """ a collection of pieces that share the same locations, same orchestra, etc...
     """
-    def __init__(self, piece_desc_dir, scans_dir, stubs_dir, prints_dir, orchestra):
+    piece_desc_dir: Path
+    scans_dir: Path
+    stubs_dir: Path
+    prints_dir: Path
+    orchestra: Orchestra
+
+    def __init__(self, piece_desc_dir: Path, scans_dir: Path, stubs_dir: Path, prints_dir: Path, orchestra: Orchestra):
         """
         Parammeters
         -----------
diff --git a/src/pymusco/tsauto.py b/src/pymusco/tsauto.py
index 59a86d0..d2f0cbe 100644
--- a/src/pymusco/tsauto.py
+++ b/src/pymusco/tsauto.py
@@ -4,12 +4,13 @@
 @author: graffy
 '''
 
+from pathlib import Path
 from .core import ITrackSelector
 from .core import Track
 from .core import load_commented_json
 
 
-def load_musician_count(musician_count_file_path):
+def load_musician_count(musician_count_file_path: Path):
     return load_commented_json(musician_count_file_path)