string formatting: engineering notation

[Darren Dale]

Does anyone know if it is possible to represent a number as a string with
engineering notation (like scientific notation, but with 10 raised to
multiples of 3: 120e3, 12e-6, etc.). I know this is possible with the
decimal.Decimal class, but repeatedly instantiating Decimals is inefficient
for my application (matplotlib plotting library). If it is not currently
possible, do you think the python devs would be receptive to including
support for engineering notation in future releases?

Thanks,
Darren

[Steve Holden]

Darren Dale wrote:

Does anyone know if it is possible to represent a number as a string with
engineering notation (like scientific notation, but with 10 raised to
multiples of 3: 120e3, 12e-6, etc.). I know this is possible with the
decimal.Decimal class, but repeatedly instantiating Decimals is inefficient
for my application (matplotlib plotting library). If it is not currently
possible, do you think the python devs would be receptive to including
support for engineering notation in future releases?

How close is this:

>>"%.3e" % 3.14159

'3.142e+00'

regards
Steve
--
Steve Holden [phone] [phone]
Holden Web LLC/Ltd http://www.holdenweb.com
Skype: holdenweb http://del.icio.us/steve.holden
Blog of Note: http://holdenweb.blogspot.com
See you at PyCon? http://us.pycon.org/TX2007

[Darren Dale]

Steve Holden wrote:

Darren Dale wrote:

>Does anyone know if it is possible to represent a number as a string with
engineering notation (like scientific notation, but with 10 raised to
multiples of 3: 120e3, 12e-6, etc.). I know this is possible with the
decimal.Decimal class, but repeatedly instantiating Decimals is
inefficient for my application (matplotlib plotting library). If it is
not currently possible, do you think the python devs would be receptive
to including support for engineering notation in future releases?

How close is this:

>>"%.3e" % 3.14159

'3.142e+00'

>>"%.3e" % 31415.9

'3.142e+04'

What I am looking for is '31.4159e+03'

Darren

[Grant Edwards]

On 2007-03-14, Steve Holden <st***@holdenweb.comwrote:

Darren Dale wrote:

>Does anyone know if it is possible to represent a number as a string with
engineering notation (like scientific notation, but with 10 raised to
multiples of 3: 120e3, 12e-6, etc.). I know this is possible with the
decimal.Decimal class, but repeatedly instantiating Decimals is inefficient
for my application (matplotlib plotting library). If it is not currently
possible, do you think the python devs would be receptive to including
support for engineering notation in future releases?

How close is this:

>>"%.3e" % 3.14159

'3.142e+00'

Not close at all. It should be "3.14159"

>>"%.3e" % 31.4159

'3.142e+01'

should be 31.4159

>>"%.3e" % 314.159

'3.142e+02'

should be 314.159

>>"%.3e" % 31415.9

'3.142e+04'

should be 31.4159e3

--
Grant Edwards grante Yow! LOU GRANT froze
at my ASSETS!!
visi.com

[Jorge Godoy]

Steve Holden <st***@holdenweb.comwrites:

Darren Dale wrote:

>Does anyone know if it is possible to represent a number as a string with
engineering notation (like scientific notation, but with 10 raised to
multiples of 3: 120e3, 12e-6, etc.). I know this is possible with the
decimal.Decimal class, but repeatedly instantiating Decimals is inefficient
for my application (matplotlib plotting library). If it is not currently
possible, do you think the python devs would be receptive to including
support for engineering notation in future releases?

How close is this:

>>"%.3e" % 3.14159

'3.142e+00'

>>"%.3e" % 314159

'3.142e+05'

>>>

Not close when you have the exponent.

--
Jorge Godoy <jg****@gmail.com>

[attn.steven.kuo]

On Mar 14, 1:14 pm, Darren Dale <[e-mail]:

Does anyone know if it is possible to represent a number as a string with
engineering notation (like scientific notation, but with 10 raised to
multiples of 3: 120e3, 12e-6, etc.). I know this is possible with the
decimal.Decimal class, but repeatedly instantiating Decimals is inefficient
for my application (matplotlib plotting library). If it is not currently
possible, do you think the python devs would be receptive to including
support for engineering notation in future releases?

Do you also consider this to be too inefficient?
import math

for exponent in xrange(-10, 11):
flt = 1.23 * math.pow(10, exponent)
l = math.log10(flt)
if l < 0:
l = l - 3
p3 = int(l / 3) * 3
multiplier = flt / pow(10, p3)
print '%e =%fe%d' % (flt, multiplier, p3)

--
Hope this helps,
Steven

[Darren Dale]

at*************@gmail.com wrote:

On Mar 14, 1:14 pm, Darren Dale <[e-mail]:

>Does anyone know if it is possible to represent a number as a string with
engineering notation (like scientific notation, but with 10 raised to
multiples of 3: 120e3, 12e-6, etc.). I know this is possible with the
decimal.Decimal class, but repeatedly instantiating Decimals is
inefficient for my application (matplotlib plotting library). If it is
not currently possible, do you think the python devs would be receptive
to including support for engineering notation in future releases?

Do you also consider this to be too inefficient?
import math

for exponent in xrange(-10, 11):
flt = 1.23 * math.pow(10, exponent)
l = math.log10(flt)
if l < 0:
l = l - 3
p3 = int(l / 3) * 3
multiplier = flt / pow(10, p3)
print '%e =%fe%d' % (flt, multiplier, p3)

That's a good suggestion. It's probably fast enough. I was hoping that
something like '%n'%my_number already existed.