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gh-118164: str(10**10000) hangs if the C _decimal module is missing (#118503)

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* Initial stab.

* Test the tentative fix. Hangs "forever" without this change.

* Move the new test to a better spot.

* New comment to explain why _convert_to_str allows any poewr of 10.

* Fixed a comment, and fleshed out an existing test that appeared unfinished.

* Added temporary asserts. Or maybe permanent ;-)

* Update Lib/_pydecimal.py

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

* Remove the new _convert_to_str().

Serhiy and I independently concluded that exact powers of 10
aren't possible in these contexts, so just checking the
string length is sufficient.

* At least for now, add the asserts to the other block too.

* 📜🤖 Added by blurb_it.

---------

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
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Tim Peters 2024-05-04 18:22:33 -05:00 • committed by GitHub
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3 changed files with 40 additions and 5 deletions
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19
Lib/_pydecimal.py
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@ -2131,10 +2131,16 @@ def _power_exact(self, other, p):
else:
return None
if xc >= 10**p:
# An exact power of 10 is representable, but can convert to a
# string of any length. But an exact power of 10 shouldn't be
# possible at this point.
assert xc > 1, self
assert xc % 10 != 0, self
strxc = str(xc)
if len(strxc) > p:
return None
xe = -e-xe
return _dec_from_triple(0, str(xc), xe)
return _dec_from_triple(0, strxc, xe)
# now y is positive; find m and n such that y = m/n
if ye >= 0:
@ -2184,13 +2190,18 @@ def _power_exact(self, other, p):
return None
xc = xc**m
xe *= m
if xc > 10**p:
# An exact power of 10 is representable, but can convert to a string
# of any length. But an exact power of 10 shouldn't be possible at
# this point.
assert xc > 1, self
assert xc % 10 != 0, self
str_xc = str(xc)
if len(str_xc) > p:
return None
# by this point the result *is* exactly representable
# adjust the exponent to get as close as possible to the ideal
# exponent, if necessary
str_xc = str(xc)
if other._isinteger() and other._sign == 0:
ideal_exponent = self._exp*int(other)
zeros = min(xe-ideal_exponent, p-len(str_xc))