为什么在格式字符串中%e的行为与%g不同？

Question

尝试过Python3号：

为什么这些格式字符串返回的数字精度不同？在

>>> "%.3e" % 123456789
'1.235e+08' 
>>> "%.3g" % 123456789
'1.23e+08' 

Answer 1

从python文档中：

'e' Exponent notation. Prints the number in scientific notation using the letter ‘e’ to indicate the exponent. The default precision is 6.

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'g'
General format. For a given precision p >= 1, this rounds the number to p significant digits and then formats the result in either fixed-point format or in scientific notation, depending on its magnitude.

The precise rules are as follows: suppose that the result formatted with presentation type 'e' and precision p-1 would have exponent exp. Then if -4 <= exp < p, the number is formatted with presentation type 'f' and precision p-1-exp. Otherwise, the number is formatted with presentation type 'e' and precision p-1. In both cases insignificant trailing zeros are removed from the significand, and the decimal point is also removed if there are no remaining digits following it.

Positive and negative infinity, positive and negative zero, and nans, are formatted as inf, -inf, 0, -0 and nan respectively, regardless of the precision.

A precision of 0 is treated as equivalent to a precision of 1. The default precision is 6.

其他值：

>>> "%.3e" % 123
'1.230e+02'
>>> "%.3g" % 123
'123'
>>> "%.3e" % 1234
'1.234e+03'
>>> "%.3g" % 1234
'1.23e+03'

那么精确性是如何明确规定的。g似乎使用精度作为精度的常规定义，而{}使用小数点后的位数。在