Working implementation

reference.py

@@ -0,0 +1,50 @@
+#!/usr/bin/env python3
+import sys
+
+# Creates an iterator that loops a list indefinitely
+class LoopList:
+    def __init__(self, ls):
+        self.ls = ls
+    def __iter__(self):
+        self.i = 0
+        return self
+    def __next__(self):
+        v = self.ls[self.i]
+        self.i = (self.i + 1) % len(self.ls)
+        return v
+
+def splitAt(w,n):
+    for i in range(0,len(w),n):
+        yield w[i:i+n]
+
+# computes checkdigit for invoice number
+# https://www.pangaliit.ee/settlements-and-standards/reference-number-of-the-invoice
+def checkdigit(ref):
+    ref = str(ref)
+    weights = [7,3,1]
+    wref = [int(x[0])*int(x[1]) for x in zip(ref[::-1], LoopList(weights))]
+    wsum = sum(wref)
+    checkdigit = 10 - (wsum % 10)
+    return str(checkdigit)[-1]
+
+# https://github.com/terokallio/reference-numbers/blob/master/src/main/java/com/terokallio/referencenumbers/RFCreditorReference.java
+def isocheckdigits(ref):
+    #       ref + "RF"   + "00"
+    #        |      |       |
+    #        v      v       v
+    magic = ref + '2715' + '00'
+    mod = int(magic) % 97
+    check = 98 - mod
+    return '0' + str(check) if check < 10 else str(check)
+
+def convert(ref):
+    refc = ref + checkdigit(ref)
+    print('Reference with checkdigit: \n\t', refc)
+
+    refiso = 'RF' + isocheckdigits(refc) + refc
+    refiso = " ".join(splitAt(refiso,4))
+    print('ISO 11649 converted reference: \n\t', refiso)
+
+if __name__ == '__main__':
+    ref = sys.argv[1]
+    convert(ref)