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I have a normal float number such as "1234.567" or "100000". I would like to convert it to a string such that the precision is fixed and the number is in scientific notation. For example, with 5 digits, the results would be "1.2346e003 and "1.0000e005", respectively. The builtin Decimal number -> string functions will round it if it can, so the second number would be only "1e005" even when I want more digits. This is undesirable since I need all numbers to be the same length.

Is there a "pythonic" way to do this without resorting to complicated string operations?

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3 Answers 3

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precision = 2 number_to_convert = 10000 print "%0.*e"%(precision,number_to_convert)

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You can use the %e string formatter:

>>> '%1.5e'%1234.567 '1.23457e+03' >>> "%1.5e"%100000 '1.00000e+05'

%x.ye where x = min characters and y = max precision.

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ahhh you fixed it before I posted ... (+1)
Yeah I missed the same length part for whatever reason. All good thx.
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If you need to keep the 3-digit exponent like in your example, you can define your own function. Here's an example adapted from this answer:

def eformat(f, prec, exp_digits): s = "%.*e"%(prec, f) mantissa, exp = s.split('e') return "%se%0*d"%(mantissa, exp_digits, int(exp)) >>> print eformat(1234.567, 4, 3) 1.2346e003
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yes a three digit is good because 1e200 is not longer than 1e20.

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