float formatting

[Peter Otten]

Brian wrote:

> I am a bit stuck with a float formatting issue.  What I want to do is
> print a float to the screen with each line showing one more decimal
> place.  Here is a code snip that may explain it better:
> 
> #!/usr/bin/env python
> 
> num1 = 32
> num2 = 42.98765
> 
> for i in range(2,7):
> print "|" + "%10.3f" % num2 + "|"
> 
> In the for loop, is the line with my difficulty.  In a perfect world it
> would read something like this:
> 
> for i in range(2,7):
>     print "|" + "%10.if" % num2 + "|"  #where i would be the iteration
> and the num of decimal places
> 
> However, if I do that I get errors saying that all args were not
> converted during string formatting.  An escaped 'i' does not work
> either.

In the http://en.wikipedia.org/wiki/Best_of_all_possible_worlds you have to
use a '*' instead of the 'i':

>>> for i in range(2, 7):
...     print "|%10.*f|" % (i, 42.98765)
...
|     42.99|
|    42.988|
|   42.9877|
|  42.98765|
| 42.987650|

You can replace the width constant with a star, too:

>>> "|%*.*f|" % (10, 3, 1.23456)
'|     1.235|'

See http://docs.python.org/lib/typesseq-strings.html for the full story.

Peter