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gh-72902: improve Fraction(str) speed (don't use regexp's) #133994

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gh-72902: improve Fraction(str) speed (don't use regexp's) #133994

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b45b672
gh-72902: improve Fraction(str) speed (don't use regexp's)
skirpichev May 1, 2025
d6b0083
Update Lib/fractions.py
skirpichev May 14, 2025
05e9110
+ a quick fix
skirpichev May 15, 2025
7c567fc
Update Lib/fractions.py
skirpichev May 16, 2025
cb679a0
Merge branch 'master' into speedup-Fraction-fromstr/72902
skirpichev May 19, 2025
e383bdb
address review: add test
skirpichev May 19, 2025
a617212
Merge branch 'master' into speedup-Fraction-fromstr/72902
skirpichev May 20, 2025
48f73f0
+ revert moving numbers.Rational check
skirpichev May 20, 2025
20436d8
+1
skirpichev May 20, 2025
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89 changes: 51 additions & 38 deletions Lib/fractions.py
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Original file line number Diff line number Diff line change
Expand Up @@ -53,20 +53,6 @@ def _hash_algorithm(numerator, denominator):
result = hash_ if numerator >= 0 else -hash_
return -2 if result == -1 else result

_RATIONAL_FORMAT = re.compile(r"""
\A\s* # optional whitespace at the start,
(?P<sign>[-+]?) # an optional sign, then
(?=\d|\.\d) # lookahead for digit or .digit
(?P<num>\d*|\d+(_\d+)*) # numerator (possibly empty)
(?: # followed by
(?:\s*/\s*(?P<denom>\d+(_\d+)*))? # an optional denominator
| # or
(?:\.(?P<decimal>\d*|\d+(_\d+)*))? # an optional fractional part
(?:E(?P<exp>[-+]?\d+(_\d+)*))? # and optional exponent
)
\s*\z # and optional whitespace to finish
""", re.VERBOSE | re.IGNORECASE)


# Helpers for formatting

Expand Down Expand Up @@ -252,31 +238,58 @@ def __new__(cls, numerator=0, denominator=None):

elif isinstance(numerator, str):
# Handle construction from strings.
m = _RATIONAL_FORMAT.match(numerator)
if m is None:
raise ValueError('Invalid literal for Fraction: %r' %
numerator)
numerator = int(m.group('num') or '0')
denom = m.group('denom')
if denom:
denominator = int(denom)
else:
denominator = 1
decimal = m.group('decimal')
if decimal:
decimal = decimal.replace('_', '')
scale = 10**len(decimal)
numerator = numerator * scale + int(decimal)
denominator *= scale
exp = m.group('exp')
if exp:
exp = int(exp)
if exp >= 0:
numerator *= 10**exp
fraction_literal = numerator
num, is_fraction_format, denom = fraction_literal.partition('/')
try:
num = num.strip()
denom = denom.strip()
if num and denom and denom[0].isdigit():
denominator = int(denom)
numerator = int(num)
elif num and not is_fraction_format:
denominator = 1
num, is_exp_format, exp = num.replace('E', 'e').partition('e')
if is_exp_format and not exp:
raise ValueError
num, _, decimal = num.partition('.')
if num:
if num[0] in ('+', '-'):
sign = num[0] == '-'
num = num[1:]
else:
sign = 0
if num and not (num[-1].isdigit() and num[0].isdigit()):
raise ValueError
else:
denominator *= 10**-exp
if m.group('sign') == '-':
numerator = -numerator
sign = 0
if decimal:
if not decimal[0].isdigit() or not decimal[-1].isdigit():
raise ValueError
numerator = int(num or '0')
decimal_len = len(decimal.replace('_', ''))
decimal = int(decimal)
scale = 10**decimal_len
numerator = numerator*scale + decimal
denominator *= scale
else:
numerator = int(num)
if sign:
numerator = -numerator
if exp:
if not (exp[0] in ('+', '-') or exp[0].isdigit()):
raise ValueError
exp = int(exp)
if exp >= 0:
numerator *= 10**exp
else:
denominator *= 10**-exp
else:
raise ValueError
except ValueError as exc:
if exc.args and re.match('^Exceeds', exc.args[0]):
raise
raise ValueError('Invalid literal for Fraction: %r' %
fraction_literal)

else:
raise TypeError("argument should be a string or a Rational "
Expand Down
2 changes: 2 additions & 0 deletions Lib/test/test_fractions.py
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Original file line number Diff line number Diff line change
Expand Up @@ -434,6 +434,7 @@ def check_invalid(s):
# Imitate float's parsing.
check_invalid("+ 3/2")
check_invalid("- 3/2")
check_invalid("+ 343.33")
# Avoid treating '.' as a regex special character.
check_invalid("3a2")
# Don't accept combinations of decimals and rationals.
Expand All @@ -445,6 +446,7 @@ def check_invalid(s):
# No space around e.
check_invalid("3.2 e1")
check_invalid("3.2e 1")
check_invalid("232e\t2")
# Fractional part don't need a sign.
check_invalid("3.+2")
check_invalid("3.-2")
Expand Down
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2025-05-02-13-30-08.gh-issue-72902.B0BV8C.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Improve speed (x1.3-1.5) of the :class:`~fractions.Fraction` constructor for
string inputs.
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