float formatting

[Brian]

Hello all,

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.

Any thoughts would be appreciated.

Thanks,
Brian

[Diez B. Roggisch]

Re: float formatting

> However, if I do that I get errors saying that all args were not[color=blue]
> converted during string formatting. An escaped 'i' does not work
> either.[/color]

You need to format the string twice - first, to generate the float
formatting string, and then to format the string.


Like this:

num = 7.1234567890123 4567
for i in xrange(3,7):
print ("%%.%if" % i) % num



Note the %% that produces a single % for the second string interpolation.

Diez

[Dave Hansen]

Re: float formatting

On 25 Jan 2006 11:32:27 -0800 in comp.lang.pytho n, "Brian"
<bnblazer@gmail .com> wrote:
[color=blue]
>Hello all,
>
>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
>[/color]

Try something like this
[color=blue][color=green][color=darkred]
>>> num2 = 42.98765
>>> for i in range(2,7):[/color][/color][/color]
print "|" + "%10.*f"%(i,num 2) + "|"


| 42.99|
| 42.988|
| 42.9877|
| 42.98765|
| 42.987650|[color=blue][color=green][color=darkred]
>>>[/color][/color][/color]

HTH,
-=Dave

--
Change is inevitable, progress is not.

[Peter Otten]

Re: float formatting

Brian wrote:
[color=blue]
> 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.[/color]

In the http://en.wikipedia.org/wiki/Best_of...ossible_worlds you have to
use a '*' instead of the 'i':
[color=blue][color=green][color=darkred]
>>> for i in range(2, 7):[/color][/color][/color]
.... 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:
[color=blue][color=green][color=darkred]
>>> "|%*.*f|" % (10, 3, 1.23456)[/color][/color][/color]
'| 1.235|'

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

Peter

[Tim Chase]

Re: float formatting

> for i in range(2,7):[color=blue]
> print "|" + "%10.if" % num2 + "|" #where i would be the iteration
> and the num of decimal places[/color]
[color=blue][color=green][color=darkred]
>>> for places in range(2,7):[/color][/color][/color]
... print "|%10.*f|" % (places, num2)
...
| 42.99|
| 42.988|
| 42.9877|
| 42.98765|
| 42.987654|

seems to do the trick.

It exploits the "*" operator for specifying the precision as
detailed in item #4 at

http://docs.python.org/lib/typesseq-strings.html

which is the same as in C/C++ formatting strings.

-tkc

[Brian]

Re: float formatting

Thanks guys, that really helped. Am I to assume that the * references
the args in the parens?

Thanks,
Brian

[Peter Hansen]

Re: float formatting

Brian wrote:[color=blue]
> Thanks guys, that really helped. Am I to assume that the * references
> the args in the parens?[/color]

Better than assuming, you can read all about it:

http://docs.python.org/lib/typesseq-strings.html

-Peter