Undocumented alternate form for %#f ?

[Dino Viehland]

I'm assuming this is by-design, but it doesn't appear to be documented:

'%8.f' % (-1) ' -1' '%#8.f' % (-1)

' -1.'
The docs list the alternate forms, but there isn't one listed for f/F. Itwould seem the alternate form for floating points is truncate & round the floating point value, but always display the . at the end. Is that correct?

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[Dave Hughes]

Dino Viehland wrote:

I'm assuming this is by-design, but it doesn't appear to be
documented:

'%8.f' % (-1) ' -1' '%#8.f' % (-1) ' -1.'
The docs list the alternate forms, but there isn't one listed for
f/F. It would seem the alternate form for floating points is
truncate & round the floating point value, but always display the .
at the end. Is that correct?

The Python % operator follows the C sprintf function pretty darn
closely in behaviour (hardly surprising really, though I've never
peeked at the implementation) . Hence "man sprintf" can provide some
clues here. From man sprintf on my Linux box:

#
The value should be converted to an ``alternate form''. For o
conversions, the first character of the output string is made
zero (by prefixing a 0 if it was not zero already). For x and X
conversions, a non-zero result has the string `0x' (or `0X' for
X conversions) prepended to it. For a, A, e, E, f, F, g, and G
conversions, the result will always contain a decimal point,
even if no digits follow it (normally, a decimal point appears
in the results of those conversions only if a digit follows).
For g and G conversions, trailing zeros are not removed from the
result as they would otherwise be. For other conversions, the
result is undefined.

Hence, I don't think it's the # doing the truncating here, but it
certainly is producing the mandatory decimal point. If you get rid of
the "." in the specification, it uses the default decimal precision (6):

"%8f" % (-1) '-1.000000' "%#8f" % (-1)

'-1.000000'

No difference with the alternate specification here as the precision is
non-zero. Again, from man sprintf:

The precision
[snip]
If the precision is given as
just `.', or the precision is negative, the precision is taken to be
zero. This gives the minimum number of digits to appear for d, i, o,
u, x, and X conversions, the number of digits to appear after the radix
character for a, A, e, E, f, and F conversions, the maximum number of
significant digits for g and G conversions, or the maximum number of
characters to be printed from a string for s and S conversions.
HTH,

Dave.
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