diff --git a/src/mdevaluate/checksum.py b/src/mdevaluate/checksum.py
index a10ad3f..8a234eb 100755
--- a/src/mdevaluate/checksum.py
+++ b/src/mdevaluate/checksum.py
@@ -3,6 +3,7 @@ import hashlib
 from .logging import logger
 from types import ModuleType, FunctionType
 import inspect
+from typing import Iterable
 
 import numpy as np
 
@@ -11,7 +12,7 @@ import numpy as np
 SALT = 42
 
 
-def version(version_nr, calls=[]):
+def version(version_nr: int, calls: Iterable = ()):
     """Function decorator that assigns a custom checksum to a function."""
 
     def decorator(func):
@@ -27,7 +28,7 @@ def version(version_nr, calls=[]):
     return decorator
 
 
-def strip_comments(s):
+def strip_comments(s: str):
     """Strips comment lines and docstring from Python source string."""
     o = ""
     in_docstring = False
@@ -43,14 +44,15 @@ def checksum(*args, csum=None):
     """
     Calculate a checksum of any object, by sha1 hash.
 
-    Input for the hash are some salt bytes and the byte encoding of a string
+    Inputs for the hash are some salt bytes and the byte encoding of a string
     that depends on the object and its type:
 
-    - If a method __checksum__ is available, it's return value is converted to bytes
+    - If a method __checksum__ is available, its return value is converted to bytes
     - str or bytes are used as sha1 input directly
     - modules use the __name__ attribute
     - functions use the function code and any closures of the function
-    - functools.partial uses the checksum of the function and any arguments, that were defined
+    - functools.partial uses the checksum of the function and any arguments, that were
+        defined
     - numpy.ndarray uses bytes representation of the array (arr.tobytes())
     - Anything else is converted to a str
     """