#!/usr/bin/env python
# cardinal_pythonlib/nhs.py
"""
===============================================================================
Original code copyright (C) 2009-2022 Rudolf Cardinal (rudolf@pobox.com).
This file is part of cardinal_pythonlib.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
https://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
===============================================================================
**Support functions regarding NHS numbers, etc.**
"""
import re
import random
from typing import List, Optional, Union
from cardinal_pythonlib.logs import get_brace_style_log_with_null_handler
log = get_brace_style_log_with_null_handler(__name__)
# =============================================================================
# NHS number validation
# =============================================================================
NHS_DIGIT_WEIGHTINGS = [10, 9, 8, 7, 6, 5, 4, 3, 2]
[docs]def nhs_check_digit(ninedigits: Union[str, List[Union[str, int]]]) -> int:
"""
Calculates an NHS number check digit.
Args:
ninedigits: string or list
Returns:
check digit
Method:
1. Multiply each of the first nine digits by the corresponding
digit weighting (see :const:`NHS_DIGIT_WEIGHTINGS`).
2. Sum the results.
3. Take remainder after division by 11.
4. Subtract the remainder from 11
5. If this is 11, use 0 instead
If it's 10, the number is invalid
If it doesn't match the actual check digit, the number is invalid
This function will return 10 for some values, but that is invalid; it's up
to the caller to check.
"""
if len(ninedigits) != 9 or not all(str(x).isdigit() for x in ninedigits):
raise ValueError("bad string to nhs_check_digit")
check_digit = 11 - (
sum([int(d) * f for (d, f) in zip(ninedigits, NHS_DIGIT_WEIGHTINGS)])
% 11
)
# ... % 11 yields something in the range 0-10
# ... 11 - that yields something in the range 1-11
if check_digit == 11:
check_digit = 0
return check_digit
[docs]def is_valid_nhs_number(n: int) -> bool:
"""
Validates an integer as an NHS number.
Args:
n: NHS number
Returns:
valid?
Checksum details are at
https://web.archive.org/web/20180311083424/https://www.datadictionary.nhs.uk/version2/data_dictionary/data_field_notes/n/nhs_number_de.asp;
https://web.archive.org/web/20220503215904/https://www.datadictionary.nhs.uk/attributes/nhs_number.html
""" # noqa
if not isinstance(n, int):
log.debug("is_valid_nhs_number: parameter was not of integer type")
return False
s = str(n)
# Not 10 digits long?
if len(s) != 10:
# Note that this excludes anything with a leading 0.
log.debug("is_valid_nhs_number: not 10 digits")
return False
main_digits = [int(s[i]) for i in range(9)]
actual_check_digit = int(s[9]) # tenth digit
expected_check_digit = nhs_check_digit(main_digits)
if expected_check_digit == 10:
log.debug("is_valid_nhs_number: calculated check digit invalid")
return False
if expected_check_digit != actual_check_digit:
log.debug("is_valid_nhs_number: check digit mismatch")
return False
# Hooray!
return True
[docs]def generate_random_nhs_number(official_test_range: bool = True) -> int:
"""
Returns a random valid NHS number, as an ``int``.
Args:
official_test_range:
Make it start with "999", the official NHS test range. See
https://digital.nhs.uk/services/e-referral-service/document-library/synthetic-data-in-live-environments,
saved at
https://web.archive.org/web/20210116183039/https://digital.nhs.uk/services/e-referral-service/document-library/synthetic-data-in-live-environments.
""" # noqa
check_digit = 10 # NHS numbers with this check digit are all invalid
while check_digit == 10:
if official_test_range:
# Make it start with 999.
digits = [9, 9, 9] # don't start with a zero
digits.extend([random.randint(0, 9) for _ in range(6)])
else:
# Any NHS number. Could potentially be a real one.
digits = [random.randint(1, 9)] # don't start with a zero
digits.extend([random.randint(0, 9) for _ in range(8)])
# ... length now 9
check_digit = nhs_check_digit(digits)
# noinspection PyUnboundLocalVariable
digits.append(check_digit)
return int("".join([str(d) for d in digits]))
[docs]def is_test_nhs_number(n: int) -> bool:
"""
Is this number both valid and in the official test range (starting 999)?
See reference above.
"""
return is_valid_nhs_number(n) and str(n)[:3] == "999"
[docs]def test_nhs_rng(n: int = 100) -> None:
"""
Tests the NHS random number generator.
"""
for i in range(n):
x = generate_random_nhs_number()
assert is_valid_nhs_number(x), f"Invalid NHS number: {x}"
[docs]def generate_nhs_number_from_first_9_digits(
first9digits: str,
) -> Optional[int]:
"""
Returns a valid NHS number, as an ``int``, given the first 9 digits.
The particular purpose is to make NHS numbers that *look* fake (rather
than truly random NHS numbers which might accidentally be real).
For example:
.. code-block:: none
123456789_ : no; checksum 10
987654321_ : yes, valid if completed to 9876543210
999999999_ : yes, valid if completed to 9999999999
But see also :func:`generate_random_nhs_number` with its option to use the
official NHS test range.
"""
if len(first9digits) != 9:
log.warning("Not 9 digits")
return None
try:
first9int = int(first9digits)
except (TypeError, ValueError):
log.warning("Not an integer")
return None # not an int
if len(str(first9int)) != len(first9digits):
# e.g. leading zeros, or some such
log.warning("Leading zeros?")
return None
check_digit = nhs_check_digit(first9digits)
if check_digit == 10: # NHS numbers with this check digit are all invalid
log.warning("Can't have check digit of 10")
return None
return int(first9digits + str(check_digit))
# =============================================================================
# Get an NHS number out of text
# =============================================================================
WHITESPACE_REGEX = re.compile(r"\s")
NON_NUMERIC_REGEX = re.compile("[^0-9]") # or "\D"
[docs]def nhs_number_from_text_or_none(s: str) -> Optional[int]:
"""
Returns a validated NHS number (as an integer) from a string, or ``None``
if it is not valid.
It's a 10-digit number, so note that database 32-bit INT values are
insufficient; use BIGINT. Python will handle large integers happily.
NHS number rules:
https://www.datadictionary.nhs.uk/version2/data_dictionary/data_field_notes/n/nhs_number_de.asp?shownav=0
""" # noqa
# None in, None out.
funcname = "nhs_number_from_text_or_none: "
if not s:
log.debug(funcname + "incoming parameter was None")
return None
# (a) If it's not a 10-digit number, bye-bye.
# Remove whitespace
s = WHITESPACE_REGEX.sub("", s) # replaces all instances
# Contains non-numeric characters?
if NON_NUMERIC_REGEX.search(s):
log.debug(funcname + "contains non-numeric characters")
return None
# Not 10 digits long?
if len(s) != 10:
log.debug(funcname + "not 10 digits long")
return None
# (b) Validation
n = int(s)
if not is_valid_nhs_number(n):
log.debug(funcname + "failed validation")
return None
# Happy!
return n