Creating French BBAN (RIB) checksum algorithm

schwifty/checksum/__init__.py

@@ -38,3 +38,4 @@ def register(algorithm_cls: Type[Algorithm], prefix: Optional[str] = None) -> Ty
 from schwifty.checksum import belgium  # noqa
 from schwifty.checksum import germany  # noqa
 from schwifty.checksum import italy  # noqa
+from schwifty.checksum import france  # noqa

schwifty/checksum/france.py

@@ -0,0 +1,45 @@
+import functools
+
+from schwifty import checksum
+from schwifty import registry
+
+
+register = functools.partial(checksum.register, prefix="FR")
+
+CONVERT_LETTERS = {
+    '0': '0', '1': '1', '2': '2', '3': '3', '4': '4', '5': '5', '6': '6', '7': '7', '8': '8', '9': '9',
+              'A': '1', 'B': '2', 'C': '3', 'D': '4', 'E': '5', 'F': '6', 'G': '7', 'H': '8', 'I': '9',
+              'J': '1', 'K': '2', 'L': '3', 'M': '4', 'N': '5', 'O': '6', 'P': '7', 'Q': '8', 'R': '9',
+                        'S': '2', 'T': '3', 'U': '4', 'V': '5', 'W': '6', 'X': '7', 'Y': '8', 'Z': '9',
+}
+
+@register
+class DefaultAlgorithm(checksum.Algorithm):
+    name = "default"
+    accepts = checksum.InputType.BBAN
+    checksum_length = 2
+
+    def compute(self, bban: str) -> str:
+        spec = registry.get("iban")
+        assert isinstance(spec, dict)
+        bank_code = bban[spec["FR"]["positions"]["bank_code"][0]:spec["FR"]["positions"]["bank_code"][1]]
+        branch_code = bban[spec["FR"]["positions"]["branch_code"][0]:spec["FR"]["positions"]["branch_code"][1]]
+        account_code = bban[spec["FR"]["positions"]["account_code"][0]:spec["FR"]["positions"]["account_code"][1]]
+
+        num_bank_code = ''
+        for bank_code_char in bank_code:
+            num_bank_code = num_bank_code + CONVERT_LETTERS[bank_code_char]
+
+        num_branch_code = ''
+        for branch_code_char in branch_code:
+            num_branch_code = num_branch_code + CONVERT_LETTERS[branch_code_char]
+
+        num_account_code = ''
+        for account_code_char in account_code:
+            num_account_code = num_account_code + CONVERT_LETTERS[account_code_char]
+
+        checksum = 97 -((89 * int(num_bank_code) + 15 * int(num_branch_code) + 3 * int(num_account_code)) % 97)
+        return str(checksum).zfill(self.checksum_length)
+
+    def validate(self, bban: str) -> bool:
+        return bban[-self.checksum_length :] == self.compute(bban[: -self.checksum_length])

schwifty/iban.py

@@ -52,6 +52,9 @@ def add_bban_checksum(country_code: str, bban: str) -> str:
         bban = bban[:3] + bban[5:]
         checksum = algorithms["BE:default"].compute(bban)
         bban = bban + checksum
+    elif country_code == "FR":
+        checksum = algorithms["FR:default"].compute(bban)
+        bban = bban[0:21] + checksum
     return bban
 
 

schwifty/iban_registry/generated.json

@@ -486,16 +486,16 @@
     "iban_length": 27,
     "positions": {
       "account_code": [
-        5,
-        23
+        10,
+        21
       ],
       "bank_code": [
         0,
         5
       ],
       "branch_code": [
         5,
-        5
+        10
       ]
     }
   },
@@ -1899,4 +1899,4 @@
       ]
     }
   }
-}
+}