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bpo-44258: support PEP 515 for Fraction's initialization from string (GH-26422)

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* bpo-44258: support PEP 515 for Fraction's initialization from string

* regexps's version

* A different regexps version, which doesn't suffer from catastrophic backtracking

* revert denom -> den

* strip "_" from the decimal str, add few tests

* drop redundant tests

* Add versionchanged & whatsnew entry

* Amend Fraction constructor docs

* Change .. versionchanged:...
This commit is contained in:
Sergey B Kirpichev 2021-06-07 10:06:33 +03:00 • committed by GitHub
parent afb2eed72b
commit 89e50ab36f
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GPG key ID: 4AEE18F83AFDEB23
5 changed files with 85 additions and 11 deletions
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21
Lib/fractions.py
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@ -21,17 +21,17 @@ _PyHASH_MODULUS = sys.hash_info.modulus
_PyHASH_INF = sys.hash_info.inf
_RATIONAL_FORMAT = re.compile(r"""
\A\s* # optional whitespace at the start, then
(?P<sign>[-+]?) # an optional sign, then
(?=\d|\.\d) # lookahead for digit or .digit
(?P<num>\d*) # numerator (possibly empty)
(?: # followed by
(?:/(?P<denom>\d+))? # an optional denominator
| # or
(?:\.(?P<decimal>\d*))? # an optional fractional part
(?:E(?P<exp>[-+]?\d+))? # and optional exponent
\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
(?:/(?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
\s*\Z # and optional whitespace to finish
""", re.VERBOSE | re.IGNORECASE)
@ -122,6 +122,7 @@ class Fraction(numbers.Rational):
denominator = 1
decimal = m.group('decimal')
if decimal:
decimal = decimal.replace('_', '')
scale = 10**len(decimal)
numerator = numerator * scale + int(decimal)
denominator *= scale