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fix(finance): isin() actually validates the check digit #468

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30 changes: 18 additions & 12 deletions src/validators/finance.py
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Original file line number Diff line number Diff line change
Expand Up @@ -32,21 +32,27 @@ def _cusip_checksum(cusip: str):


def _isin_checksum(value: str):
check, val = 0, None
if not (value[:2].isalpha() and value[-1].isdigit()):
return False

for idx in range(12):
c = value[idx]
if c >= "0" and c <= "9" and idx > 1:
val = ord(c) - ord("0")
elif c >= "A" and c <= "Z":
val = 10 + ord(c) - ord("A")
elif c >= "a" and c <= "z":
val = 10 + ord(c) - ord("a")
# Expand letters to numbers (A=10, ..., Z=35), then run the Luhn algorithm.
digits = ""
for char in value:
if char.isdigit():
digits += char
elif char.isalpha():
digits += str(10 + ord(char.upper()) - ord("A"))
else:
return False

check = 0
for idx, digit in enumerate(reversed(digits)):
val = int(digit)
if idx & 1:
val += val
val *= 2
if val > 9:
val -= 9
check += val

return (check % 10) == 0

Expand Down Expand Up @@ -82,8 +88,8 @@ def isin(value: str):
[1]: https://en.wikipedia.org/wiki/International_Securities_Identification_Number

Examples:
>>> isin('037833DP2')
ValidationError(func=isin, args={'value': '037833DP2'})
>>> isin('US0378331005')
True
>>> isin('037833DP3')
ValidationError(func=isin, args={'value': '037833DP3'})

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4 changes: 2 additions & 2 deletions tests/test_finance.py
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Original file line number Diff line number Diff line change
Expand Up @@ -24,13 +24,13 @@ def test_returns_failed_validation_on_invalid_cusip(value: str):
# ==> ISIN <== #


@pytest.mark.parametrize("value", ["US0004026250", "JP000K0VF054", "US0378331005"])
@pytest.mark.parametrize("value", ["US0004026250", "JP000K0VF055", "US0378331005"])
def test_returns_true_on_valid_isin(value: str):
"""Test returns true on valid isin."""
assert isin(value)


@pytest.mark.parametrize("value", ["010378331005", "XCVF", "00^^^1234", "A000009"])
@pytest.mark.parametrize("value", ["010378331005", "XCVF", "00^^^1234", "A000009", "US0378331004"])
def test_returns_failed_validation_on_invalid_isin(value: str):
"""Test returns failed validation on invalid isin."""
assert isinstance(isin(value), ValidationError)
Expand Down