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# romanNumerals.py
#
# Copyright (c) 2006, 2019, Paul McGuire
#
import pyparsing as pp
def roman_numeral_literal(numeral_string, value):
return (
pp.Literal(numeral_string)
.set_parse_action(pp.replace_with(value))
.leave_whitespace()
)
one = roman_numeral_literal("I", 1)
four = roman_numeral_literal("IV", 4)
five = roman_numeral_literal("V", 5)
nine = roman_numeral_literal("IX", 9)
ten = roman_numeral_literal("X", 10)
forty = roman_numeral_literal("XL", 40)
fifty = roman_numeral_literal("L", 50)
ninety = roman_numeral_literal("XC", 90)
onehundred = roman_numeral_literal("C", 100)
fourhundred = roman_numeral_literal("CD", 400)
fivehundred = roman_numeral_literal("D", 500)
ninehundred = roman_numeral_literal("CM", 900)
onethousand = roman_numeral_literal("M", 1000)
# lenient parser - passes all legal Roman numerals but does not detect illegal
# numeral = (
# onethousand
# | ninehundred
# | fivehundred
# | fourhundred
# | onehundred
# | ninety
# | fifty
# | forty
# | ten
# | nine
# | five
# | four
# | one
# )
#
# roman_numeral = numeral[1, ...].set_parse_action(sum)
# strict parser - rejects illegal Roman numerals
roman_numeral = (
onethousand[...]
+ (ninehundred | fourhundred | fivehundred[0, 1] + onehundred[0, 3])[0, 1]
+ (ninety | forty | fifty[0, 1] + ten[0, 3])[0, 1]
+ (nine | four | five[0, 1] + one[0, 3])[0, 1]
).set_parse_action(sum)
pp.autoname_elements()
# uncomment to generate railroad diagram
# roman_numeral.create_diagram("romanNumerals.html")
# unit tests
def make_roman_numeral(n):
def add_digits(n, limit, c, s):
while n >= limit:
n -= limit
s += c
return n, s
ret = ""
n, ret = add_digits(n, 1000, "M", ret)
n, ret = add_digits(n, 900, "CM", ret)
n, ret = add_digits(n, 500, "D", ret)
n, ret = add_digits(n, 400, "CD", ret)
n, ret = add_digits(n, 100, "C", ret)
n, ret = add_digits(n, 90, "XC", ret)
n, ret = add_digits(n, 50, "L", ret)
n, ret = add_digits(n, 40, "XL", ret)
n, ret = add_digits(n, 10, "X", ret)
n, ret = add_digits(n, 9, "IX", ret)
n, ret = add_digits(n, 5, "V", ret)
n, ret = add_digits(n, 4, "IV", ret)
n, ret = add_digits(n, 1, "I", ret)
return ret
def main():
# make a string of all roman numerals from I to MMMMM
tests = " ".join(make_roman_numeral(i) for i in range(1, 5000 + 1))
# parse each roman numeral, and populate map for validation below
roman_int_map = {}
for expected, (t, s, e) in enumerate(roman_numeral.scan_string(tests), start=1):
orig = tests[s:e]
assert t[0] == expected, f"==> Incorrect result for {orig}: {t}"
roman_int_map[orig] = t[0]
def verify_value(s, tokens):
expected_value = roman_int_map[s]
if tokens[0] != expected_value:
raise Exception(
f"incorrect value for {s} ({tokens[0]}), expected {expected_value}"
)
success1, _ = roman_numeral.runTests(
"""\
XVI
XXXIX
XIV
XIX
MCMLXXX
MMVI
MMMMM
""",
parse_all=True,
post_parse=verify_value,
)
assert success1, "failed to parse one or more legal Roman numerals"
print("\nRun failure tests")
success2, _ = roman_numeral.runTests(
"""\
# too many X's
XXXX
# X after XL
XLX
""",
parse_all=True,
failure_tests=True,
)
assert success2, "parsed one or more illegal Roman numerals"
if __name__ == "__main__":
main()
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