mirror of https://github.com/python/cpython
Docs: format sys.float_info properly (#108107)
- Normalise capitalisation and punctuation - Use attribute markup for named tuple attributes - Use :c:macro: markup for C macros - Use a list for the 'rounds' attribute values - Use list-table, for better .rst readability - Remove one unneeded sys.float_info.dig link Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>
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Erlend E. Aasland
GitHub
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@ -574,61 +574,82 @@ always available.
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programming language; see section 5.2.4.2.2 of the 1999 ISO/IEC C standard
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[C99]_, 'Characteristics of floating types', for details.
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.. tabularcolumns:: |l|l|L|
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.. list-table:: Attributes of the :data:`!float_info` :term:`named tuple`
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:header-rows: 1
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+---------------------+---------------------+--------------------------------------------------+
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| attribute | float.h macro | explanation |
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+=====================+=====================+==================================================+
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| ``epsilon`` | ``DBL_EPSILON`` | difference between 1.0 and the least value |
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| | | greater than 1.0 that is representable as a float|
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| | | |
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| | | See also :func:`math.ulp`. |
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+---------------------+---------------------+--------------------------------------------------+
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| ``dig`` | ``DBL_DIG`` | maximum number of decimal digits that can be |
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| | | faithfully represented in a float; see below |
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+---------------------+---------------------+--------------------------------------------------+
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| ``mant_dig`` | ``DBL_MANT_DIG`` | float precision: the number of base-``radix`` |
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| | | digits in the significand of a float |
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+---------------------+---------------------+--------------------------------------------------+
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| ``max`` | ``DBL_MAX`` | maximum representable positive finite float |
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+---------------------+---------------------+--------------------------------------------------+
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| ``max_exp`` | ``DBL_MAX_EXP`` | maximum integer *e* such that ``radix**(e-1)`` is|
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| | | a representable finite float |
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+---------------------+---------------------+--------------------------------------------------+
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| ``max_10_exp`` | ``DBL_MAX_10_EXP`` | maximum integer *e* such that ``10**e`` is in the|
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| | | range of representable finite floats |
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+---------------------+---------------------+--------------------------------------------------+
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| ``min`` | ``DBL_MIN`` | minimum representable positive *normalized* float|
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| | | |
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| | | Use :func:`math.ulp(0.0) <math.ulp>` to get the |
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| | | smallest positive *denormalized* representable |
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| | | float. |
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+---------------------+---------------------+--------------------------------------------------+
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| ``min_exp`` | ``DBL_MIN_EXP`` | minimum integer *e* such that ``radix**(e-1)`` is|
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| | | a normalized float |
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+---------------------+---------------------+--------------------------------------------------+
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| ``min_10_exp`` | ``DBL_MIN_10_EXP`` | minimum integer *e* such that ``10**e`` is a |
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| | | normalized float |
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+---------------------+---------------------+--------------------------------------------------+
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| ``radix`` | ``FLT_RADIX`` | radix of exponent representation |
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+---------------------+---------------------+--------------------------------------------------+
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| ``rounds`` | ``FLT_ROUNDS`` | integer representing the rounding mode for |
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| | | floating-point arithmetic. This reflects the |
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| | | value of the system ``FLT_ROUNDS`` macro at |
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| | | interpreter startup time: |
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| | | ``-1`` indeterminable, |
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| | | ``0`` toward zero, |
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| | | ``1`` to nearest, |
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| | | ``2`` toward positive infinity, |
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| | | ``3`` toward negative infinity |
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| | | |
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| | | All other values for ``FLT_ROUNDS`` characterize |
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| | | implementation-defined rounding behavior. |
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+---------------------+---------------------+--------------------------------------------------+
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* - attribute
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- float.h macro
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- explanation
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* - .. attribute:: float_info.epsilon
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- :c:macro:`!DBL_EPSILON`
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- difference between 1.0 and the least value greater than 1.0 that is
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representable as a float.
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See also :func:`math.ulp`.
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* - .. attribute:: float_info.dig
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- :c:macro:`!DBL_DIG`
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- The maximum number of decimal digits that can be faithfully
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represented in a float; see below.
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* - .. attribute:: float_info.mant_dig
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- :c:macro:`!DBL_MANT_DIG`
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- Float precision: the number of base-``radix`` digits in the
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significand of a float.
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* - .. attribute:: float_info.max
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- :c:macro:`!DBL_MAX`
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- The maximum representable positive finite float.
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* - .. attribute:: float_info.max_exp
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- :c:macro:`!DBL_MAX_EXP`
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- The maximum integer *e* such that ``radix**(e-1)`` is a representable
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finite float.
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* - .. attribute:: float_info.max_10_exp
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- :c:macro:`!DBL_MAX_10_EXP`
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- The maximum integer *e* such that ``10**e`` is in the range of
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representable finite floats.
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* - .. attribute:: float_info.min
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- :c:macro:`!DBL_MIN`
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- The minimum representable positive *normalized* float.
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Use :func:`math.ulp(0.0) <math.ulp>` to get the smallest positive
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*denormalized* representable float.
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* - .. attribute:: float_info.min_exp
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- :c:macro:`!DBL_MIN_EXP`
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- The minimum integer *e* such that ``radix**(e-1)`` is a normalized
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float.
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* - .. attribute:: float_info.min_10_exp
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- :c:macro:`!DBL_MIN_10_EXP`
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- The minimum integer *e* such that ``10**e`` is a normalized float.
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* - .. attribute:: float_info.radix
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- :c:macro:`!FLT_RADIX`
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- The radix of exponent representation.
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* - .. attribute:: float_info.rounds
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- :c:macro:`!FLT_ROUNDS`
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- An integer representing the rounding mode for floating-point arithmetic.
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This reflects the value of the system :c:macro:`!FLT_ROUNDS` macro
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at interpreter startup time:
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* ``-1``: indeterminable
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* ``0``: toward zero
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* ``1``: to nearest
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* ``2``: toward positive infinity
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* ``3``: toward negative infinity
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All other values for :c:macro:`!FLT_ROUNDS` characterize
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implementation-defined rounding behavior.
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The attribute :attr:`sys.float_info.dig` needs further explanation. If
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``s`` is any string representing a decimal number with at most
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:attr:`sys.float_info.dig` significant digits, then converting ``s`` to a
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:attr:`!sys.float_info.dig` significant digits, then converting ``s`` to a
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float and back again will recover a string representing the same decimal
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value::
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