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bpo-30940: specify what happens if ndigits is None or omitted #3256

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bpo-30940: specify what happens if ndigits is None or omitted #3256

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e1ccc9e
Add a reference link to the regular expression objects
Aug 27, 2017
3260b04
bpo-30940: specify what happens if ndigits is None or omitted
Aug 31, 2017
86d33a1
Merge branch 'master' into issue30940
elenaoat Aug 31, 2017
ac9f872
Make the explanation more precise.
Sep 7, 2017
9cb1e24
Merge changes
Sep 7, 2017
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12 changes: 6 additions & 6 deletions Doc/library/functions.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -1297,22 +1297,22 @@ are always available. They are listed here in alphabetical order.
arguments starting at ``0``).


.. function:: round(number[, ndigits])
.. function:: round(number, ndigits=None)

Return *number* rounded to *ndigits* precision after the decimal
point. If *ndigits* is omitted or is ``None``, it returns the
point. If *ndigits* is omitted or ``None``, it returns the
nearest integer to its input.

For the built-in types supporting :func:`round`, values are rounded to the
closest multiple of 10 to the power minus *ndigits*; if two multiples are
equally close, rounding is done toward the even choice (so, for example,
both ``round(0.5)`` and ``round(-0.5)`` are ``0``, and ``round(1.5)`` is
``2``). Any integer value is valid for *ndigits* (positive, zero, or
negative). The return value is an integer if called with one argument,
otherwise of the same type as *number*.
negative). The return value is an integer if *ndigits* is omitted or is ``None``.
Otherwise the return value has the same type as *number*.

For a general Python object ``number``, ``round(number, ndigits)`` delegates to
``number.__round__(ndigits)``.
For a general Python object ``number``, ``round`` delegates to

@rhettinger rhettinger Sep 6, 2017

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Rather than lose information with this edit, I would prefer to make it more precise, "For a general Python object, round(number) or round(number, None) delegates to number.__round__(), and round(number, ndigits) delegates to number.__round__(ndigits)."

@elenaoat elenaoat Sep 7, 2017

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I've modified the text accordingly.

``number.__round__``.

.. note::

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4 changes: 2 additions & 2 deletions Python/bltinmodule.c
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Expand Up @@ -2087,10 +2087,10 @@ builtin_round(PyObject *self, PyObject *args, PyObject *kwds)
}

PyDoc_STRVAR(round_doc,
"round(number[, ndigits]) -> number\n\
"round(number, ndigits=None) -> number\n\
\n\
Round a number to a given precision in decimal digits (default 0 digits).\n\
This returns an int when called with one argument, otherwise the\n\
This returns an int when ndigits is omitted or is None, otherwise the\n\
same type as the number. ndigits may be negative.");


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