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bpo-36027: Extend three-argument pow to negative second argument (GH-13266)

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Mark Dickinson 2019-06-02 10:24:06 +01:00 • committed by GitHub
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Doc/library/functions.rst
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@ -1277,9 +1277,24 @@ are always available. They are listed here in alphabetical order.
operands, the result has the same type as the operands (after coercion)
unless the second argument is negative; in that case, all arguments are
converted to float and a float result is delivered. For example, ``10**2``
returns ``100``, but ``10**-2`` returns ``0.01``. If the second argument is
negative, the third argument must be omitted. If *z* is present, *x* and *y*
must be of integer types, and *y* must be non-negative.
returns ``100``, but ``10**-2`` returns ``0.01``.
For :class:`int` operands *x* and *y*, if *z* is present, *z* must also be
of integer type and *z* must be nonzero. If *z* is present and *y* is
negative, *x* must be relatively prime to *z*. In that case, ``pow(inv_x,
-y, z)`` is returned, where *inv_x* is an inverse to *x* modulo *z*.
Here's an example of computing an inverse for ``38`` modulo ``97``::
>>> pow(38, -1, 97)
23
>>> 23 * 38 % 97 == 1
True
.. versionchanged:: 3.8
For :class:`int` operands, the three-argument form of ``pow`` now allows
the second argument to be negative, permitting computation of modular
inverses.
.. function:: print(*objects, sep=' ', end='\\n', file=sys.stdout, flush=False)