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]

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.

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


Like this:

num = 7.12345678901234567
for i in xrange(3,7):
print ("%%.%if" % i) % num



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

Diez

 

[Dave Hansen]

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

Try something like this
print "|" + "%10.*f"%(i,num2) + "|"


| 42.99|
| 42.988|
| 42.9877|
| 42.98765|
| 42.987650|
HTH,
-=Dave

 

[Peter Otten]

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':
.... 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:
'| 1.235|'

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

Peter

 

[Tim Chase]

for i in range(2,7):

print "|" + "%10.if" % num2 + "|" #where i would be the iteration
and the num of decimal places

>>> for places in range(2,7):
... 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]

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

Thanks,
Brian

 

[Peter Hansen]

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

Better than assuming, you can read all about it:

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

-Peter