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bpo-39096: Improve description of 'e', 'f' and 'g' presentation types (GH-23537) (GH-23550) 

* Improve description of 'e', 'f' and 'g' presentation types

* Drop the 'E' from Scientific 'E' notation; remove >= 0 qualifications

* Fix false statement that the alternate form is valid for Decimal

* Nitpick: remove the Harvard/Oxford comma

* Add note that the decimal point is also removed if no digits follow it, except in alternate form
(cherry picked from commit c642374b3e)

Co-authored-by: Mark Dickinson <mdickinson@enthought.com>

Co-authored-by: Mark Dickinson <mdickinson@enthought.com>
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Miss Islington (bot) 2020-11-29 01:58:01 -08:00 committed by GitHub
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Doc/library/string.rst
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@ -384,10 +384,10 @@ following:
The ``'#'`` option causes the "alternate form" to be used for the
conversion. The alternate form is defined differently for different
types. This option is only valid for integer, float, complex and
Decimal types. For integers, when binary, octal, or hexadecimal output
types. This option is only valid for integer, float and complex
types. For integers, when binary, octal, or hexadecimal output
is used, this option adds the prefix respective ``'0b'``, ``'0o'``, or
``'0x'`` to the output value. For floats, complex and Decimal the
``'0x'`` to the output value. For float and complex the
alternate form causes the result of the conversion to always contain a
decimal-point character, even if no digits follow it. Normally, a
decimal-point character appears in the result of these conversions
@ -476,20 +476,36 @@ with the floating point presentation types listed below (except
``'n'`` and ``None``). When doing so, :func:`float` is used to convert the
integer to a floating point number before formatting.
The available presentation types for floating point and decimal values are:
The available presentation types for :class:`float` and
:class:`~decimal.Decimal` values are:
+---------+----------------------------------------------------------+
| Type | Meaning |
+=========+==========================================================+
| ``'e'`` | Exponent notation. Prints the number in scientific |
| | notation using the letter 'e' to indicate the exponent. |
| | The default precision is ``6``. |
| ``'e'`` | Scientific notation. For a given precision ``p``, |
| | formats the number in scientific notation with the |
| | letter 'e' separating the coefficient from the exponent. |
| | The coefficient has one digit before and ``p`` digits |
| | after the decimal point, for a total of ``p + 1`` |
| | significant digits. With no precision given, uses a |
| | precision of ``6`` digits after the decimal point for |
| | :class:`float`, and shows all coefficient digits |
| | for :class:`~decimal.Decimal`. If no digits follow the |
| | decimal point, the decimal point is also removed unless |
| | the ``#`` option is used. |
+---------+----------------------------------------------------------+
| ``'E'`` | Exponent notation. Same as ``'e'`` except it uses an |
| | upper case 'E' as the separator character. |
| ``'E'`` | Scientific notation. Same as ``'e'`` except it uses |
| | an upper case 'E' as the separator character. |
+---------+----------------------------------------------------------+
| ``'f'`` | Fixed-point notation. Displays the number as a |
| | fixed-point number. The default precision is ``6``. |
| ``'f'`` | Fixed-point notation. For a given precision ``p``, |
| | formats the number as a decimal number with exactly |
| | ``p`` digits following the decimal point. With no |
| | precision given, uses a precision of ``6`` digits after |
| | the decimal point for :class:`float`, and uses a |
| | precision large enough to show all coefficient digits |
| | for :class:`~decimal.Decimal`. If no digits follow the |
| | decimal point, the decimal point is also removed unless |
| | the ``#`` option is used. |
+---------+----------------------------------------------------------+
| ``'F'`` | Fixed-point notation. Same as ``'f'``, but converts |
| | ``nan`` to ``NAN`` and ``inf`` to ``INF``. |
@ -518,7 +534,10 @@ The available presentation types for floating point and decimal values are:
| | the precision. |
| | |
| | A precision of ``0`` is treated as equivalent to a |
| | precision of ``1``. The default precision is ``6``. |
| | precision of ``1``. With no precision given, uses a |
| | precision of ``6`` significant digits for |
| | :class:`float`, and shows all coefficient digits |
| | for :class:`~decimal.Decimal`. |
+---------+----------------------------------------------------------+
| ``'G'`` | General format. Same as ``'g'`` except switches to |
| | ``'E'`` if the number gets too large. The |