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gh-122450: Expand documentation for Rational and Fraction #136800

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762e14c
gh-122450: Expand numbers.Rational docstrings
skirpichev Jul 19, 2025
7e3b3dc
Merge branch 'master' into numden-props/122450
skirpichev Jul 19, 2025
478e414
Revert "gh-122450: Indicate that `Fraction` denominators are always p…
skirpichev Jul 19, 2025
c3f506a
Document Ratiomal.numerator/denominator, remove from Fraction docs
skirpichev Jul 19, 2025
12d7786
Merge branch 'master' into numden-props/122450
skirpichev Jul 21, 2025
f2aaed3
address review: more vague preable
skirpichev Jul 21, 2025
a8b6ca2
address review: 0 -> zero
skirpichev Jul 21, 2025
53e8c26
Apply suggestions from code review
skirpichev Jul 21, 2025
fb84af4
address review: restore Fraction.numerator/denominator in docs
skirpichev Jul 21, 2025
6e61673
Merge branch 'master' into numden-props/122450
skirpichev Jul 21, 2025
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10 changes: 5 additions & 5 deletions Doc/library/fractions.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -14,8 +14,8 @@
The :mod:`fractions` module provides support for rational number arithmetic.


A Fraction instance can be constructed from a pair of integers, from
another rational number, or from a string.
A Fraction instance can be constructed from a pair of numbers, from
another number, or from a string.

.. index:: single: as_integer_ratio()

Expand All @@ -25,8 +25,8 @@ another rational number, or from a string.

The first version requires that *numerator* and *denominator* are instances
of :class:`numbers.Rational` and returns a new :class:`Fraction` instance
with value equal to ``numerator/denominator`` where the denominator is positive.
If *denominator* is ``0``, it raises a :exc:`ZeroDivisionError`.
with value equal to ``numerator/denominator``. If *denominator* is zero, it
raises a :exc:`ZeroDivisionError`.
Comment on lines 26 to +29
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I still think this is worse. We now loose information that the denominator is positive, and implicitly require the user to know that {Fraction,Rational}.denominator should be positive. We are able to guarantee here that the denominator is a non-zero positive integer, there's no reason why we can't say that.

How about:

... and returns a new :class:`Fraction` instance with a value equal
to ``numerator/denominator``. The numerator and denominator of this
instance will be in the lowest terms, and the denominator will be positive.

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We now loose information that the denominator is positive, and implicitly require the user to know that {Fraction,Rational}.denominator should be positive.

No. I think that class constructor should describe it's construction, not attributes, right?

  1. This information will be present in descriptions of numerator/denominator attributes of the Fraction
  2. Or in Rational docs.

I would prefer (2) for less redundancy. But as you insist on restoring (1) - I'll do that.


The second version requires that *number* is an instance of
:class:`numbers.Rational` or has the :meth:`!as_integer_ratio` method
Expand Down Expand Up @@ -125,7 +125,7 @@ another rational number, or from a string.

.. attribute:: denominator

Denominator of the Fraction in lowest term.
Denominator of the Fraction in lowest term. Should be positive.


.. method:: as_integer_ratio()
Expand Down
4 changes: 2 additions & 2 deletions Doc/library/numbers.rst
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Expand Up @@ -69,11 +69,11 @@ The numeric tower

.. attribute:: numerator

Abstract.
Abstract. The numerator of this rational number.

.. attribute:: denominator

Abstract.
Abstract. The denominator of this rational number.


.. class:: Integral
Expand Down
11 changes: 10 additions & 1 deletion Lib/numbers.py
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Expand Up @@ -290,18 +290,27 @@ def conjugate(self):


class Rational(Real):
""".numerator and .denominator should be in lowest terms."""
"""To Real, Rational adds numerator and denominator properties.

The numerator and denominator values should be in lowest terms,
with a positive denominator.
"""

__slots__ = ()

@property
@abstractmethod
def numerator(self):
"""The numerator of a rational number in lowest terms."""
raise NotImplementedError

@property
@abstractmethod
def denominator(self):
"""The denominator of a rational number in lowest terms.

This denominator should be positive.
"""
raise NotImplementedError

# Concrete implementation of Real's conversion to float.
Expand Down
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