Document the different meaning of precision for {:f} and {:g}.
Also document how inf and nan are formatted. #3404.
diff --git a/Doc/library/string.rst b/Doc/library/string.rst
index 0e345e3..357cba3 100644
--- a/Doc/library/string.rst
+++ b/Doc/library/string.rst
@@ -387,10 +387,11 @@
character of ``'0'``.
The *precision* is a decimal number indicating how many digits should be
-displayed after the decimal point for a floating point value. For non-number
-types the field indicates the maximum field size - in other words, how many
-characters will be used from the field content. The *precision* is ignored for
-integer values.
+displayed after the decimal point for a floating point value formatted with
+``'f'`` and ``'F'``, or before and after the decimal point for a floating point
+value formatted with ``'g'`` or ``'G'``. For non-number types the field
+indicates the maximum field size - in other words, how many characters will be
+used from the field content. The *precision* is ignored for integer values.
Finally, the *type* determines how the data should be presented.
@@ -418,7 +419,7 @@
| | the current locale setting to insert the appropriate |
| | number separator characters. |
+---------+----------------------------------------------------------+
- | None | the same as ``'d'`` |
+ | None | The same as ``'d'``. |
+---------+----------------------------------------------------------+
The available presentation types for floating point and decimal values are:
@@ -439,10 +440,13 @@
+---------+----------------------------------------------------------+
| ``'g'`` | General format. This prints the number as a fixed-point |
| | number, unless the number is too large, in which case |
- | | it switches to ``'e'`` exponent notation. |
+ | | it switches to ``'e'`` exponent notation. Infinity and |
+ | | NaN values are formatted as ``inf``, ``-inf`` and |
+ | | ``nan``, respectively. |
+---------+----------------------------------------------------------+
| ``'G'`` | General format. Same as ``'g'`` except switches to |
- | | ``'E'`` if the number gets to large. |
+ | | ``'E'`` if the number gets to large. The representations |
+ | | of infinity and NaN are uppercased, too. |
+---------+----------------------------------------------------------+
| ``'n'`` | Number. This is the same as ``'g'``, except that it uses |
| | the current locale setting to insert the appropriate |
@@ -451,7 +455,7 @@
| ``'%'`` | Percentage. Multiplies the number by 100 and displays |
| | in fixed (``'f'``) format, followed by a percent sign. |
+---------+----------------------------------------------------------+
- | None | the same as ``'g'`` |
+ | None | The same as ``'g'``. |
+---------+----------------------------------------------------------+