Here is another function for human formatting:
<pre>
def sistr(value, prec=None, K=1024.0, k=1000.0, sign='', blank=' '):
'''
Convert value to a signed string with an SI prefix.
The 'prec' value specifies the number of fractional
digits to be included. Use 'prec=0' to omit any
fraction. If 'prec' is not specified or None, the
precision is adjusted to make the returned string 6
characters (without the sign).
The 'sign' character is used for positive values.
Negative values are always prefixed with '-'.
Uppercase 'K' is the scale factor for values above
1.0 and lowercase 'k' scales values below 1.0.
The 'blank' character is used as the SI prefix for
values between k and K, i.e. value without an SI
prefix. Set 'blank' to None, False or '' if no
alignment is required.
name symbol 10** symbol name
=================================
deca da + 1 - d deci
hecto h + 2 - c centi
- - - - - - - - - - - - - - - - -
Kilo K + 3 - m milli
Mega M + 6 - /u micro
Giga G + 9 - n nano
Tera T + 12 - p pico
Peta P + 15 - f femto
Exa E + 18 - a atto
Zetta Z + 21 - z zepto
Yotta Y + 24 - y yocto
---------------------------------
Xona X + 27 - x xonto
Weka W + 30 - w wekto
Vunda V + 33 - v vunkto
Uda U + 36 - u* unto
Treda TD* + 39 - td trekto
Sorta S + 42 - s sotro
Rinta R + 45 - r rimto
Quexa Q + 48 - q quekto
Pepta PP + 51 - pk pekro
Ocha O + 54 - o otro
Nena N + 57 - nk nekto
MInga MI + 60 - mk mikto
Luma L + 63 - l lunto
The prefixes below the line are non-sanctioned SI
and are only used until the symbols marked * to
avoid ambiguity. The symbols above the dotted
line are not used and '/u' is returned as 'u'.
See http://en.wikipedia.org/wiki/Binary_prefix or
http://www.bipm.org/en/si/prefixes.html and maybe
http://jimvb.home.mindspring.com/unitsystem.htm
'''
s, v, p = sign, float(value), None
if v < 0.0:
s, v = '-', -v
if v < K:
if v >= 1.0:
p = blank
elif k > 10.0:
for f in iter('munpfazyxwv'): # no unto, ...
v *= k # scale up
if v >= 1.0:
p = f
break
elif K > 10.0:
for f in iter('KMGTPEZYXWVU'): # no Treda, ...
v /= K # scale down
if v < K:
p = f
break
# format value
if p is None: # too large, small or invalid K, k
return "%.0e*" % value
elif prec is None:
if v < 100.0:
if v < 10.0:
prec = 3
else:
prec = 2
else:
if v < 1000.0:
prec = 1
else:
prec = 0
elif prec < 0:
prec = 0 # rounds
return "%s%0.*f%s" % (s, prec, v, p)
if __name__ == '__main__':
x = 17
while x < 1.0e18:
print sistr(x), x
x *= 17
x = 0.12
while x > 1.0e-18:
print sistr(x), x
x *= 0.12
</pre>
/Jean Brouwers
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