1 files changed, 12 insertions, 8 deletions
diff --git a/dedup/filemagic.py b/dedup/filemagic.py
index b71c276..a6d09ba 100644
--- a/dedup/filemagic.py
+++ b/dedup/filemagic.py
@@ -1,6 +1,8 @@
 """A very strange "hash" that uses the magic module (python3-magic) to guess
 the file type."""
 
+import typing
+
 import magic
 
 # It changed API a few times...
@@ -13,36 +15,38 @@ class FileDigester:
     """A hashlib-like class to guess a filetype using the magic module."""
     FILE_BYTES_MAX = 1024 * 1024 # copied from file source
 
-    def __init__(self):
-        self.buff = b""
-        self.identification = None
+    def __init__(self) -> None:
+        self.buff: typing.Optional[bytes] = b""
+        self.identification: typing.Optional[str] = None
 
-    def _compute_identification(self):
+    def _compute_identification(self) -> str:
+        assert self.buff is not None
         try:
             return _magic_identify(self.buff)
         except UnicodeDecodeError:
             return "magic identification is not valid UTF-8"
 
-    def update(self, buff):
+    def update(self, buff: bytes) -> None:
         if self.identification:
             return
+        assert self.buff is not None
         self.buff += buff
         if len(self.buff) >= self.FILE_BYTES_MAX:
             self.identification = self._compute_identification()
             self.buff = None
 
-    def identify(self):
+    def identify(self) -> str:
         """Return the guessed file magic identification."""
         if self.identification:
             return self.identification
         return self._compute_identification()
 
-    def hexdigest(self):
+    def hexdigest(self) -> str:
         """Compatibility with hashlib. An alias of identify. Doesn't return
         hex."""
         return self.identify()
 
-    def copy(self):
+    def copy(self) -> "FileDigester":
         new = FileDigester()
         new.buff = self.buff
         new.identification = self.identification