diff --git a/utils.py b/utils.py
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+++ b/utils.py
@@ -0,0 +1,22 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+"""
+Utility functions
+
+Karl Hoffmann,  Max Planck Institute of Molecular Cell Biology and Genetics,
+Dresden, Germany
+"""
+
+def str_filename(number, *args, **kwargs):
+    """
+    Conversion of a number (or any other object) to a string that is compatible
+    with file name syntax.
+    Based on the built-in function str(), but replaces some characters that
+    have special meaning in filenames:
+    File extension separator '.' and path separators (both slash and backslash)
+    are each replaced with underscore '_'
+    """
+    return str(number,*args,**kwargs).translate(str.maketrans({'.' : '_',
+                                                            '/' : '_',
+                                                            '\\' : '_' #note the escape to describe a single backslash
+                                                           }))
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