Is there a string format for floats which always starts with 0.x?

Question

I need a very specific string format for floats in python.

I need all numbers to look like this:

0.313575791515242E+005
0.957214231058814E+000
0.102484469467859E+002
0.251532655168561E-001
0.126906478919395E-002
-0.469847611408333E-003

They always start with a 0.x with 15 digits after the decimal point and end with 3 digits in the exponential.

Can I do this with python? I tried to look at the documentation for string formatting but couldn't figure out how.

I tried with this:

>>> number = 9.622
>>> print(f'{number:.15E}')
9.622000000000000E+00

Which is pretty close, but I still need the leading 0 and 3 digits in the exponent. It has to be like this:

0.962200000000000E+001

Any help is appreciated!

"Can I do this with python?" -- if worst comes to worst, it shouldn't be too hard to write your own function to do this, right? — Denziloe, Sep 19 '18 at 13:10
Try looking at answers on [this](https://stackoverflow.com/questions/6913532/display-a-decimal-in-scientific-notation) page — Sheldore, Sep 19 '18 at 13:24
I don't exactly know that's why I said **try**. May be the OP gets some ideas from some approaches. That's the reason, I didn't mark it as duplicate — Sheldore, Sep 19 '18 at 13:28
"**Try"** is ambiguous and can mean "this previous question provides the solutions, so try looking at it" rather than "I don't know if the solution is here but try reading all the answers and you might find something useful". — Denziloe, Sep 19 '18 at 13:37

score 2 · Accepted Answer · answered Sep 19 '18 at 13:23

2

Not sure what is the logic for -/+ before the exponent, but this should give you a good start I hope:

def format(n):
    p = 0
    while n <= -1 or n >= 1:
        n = n / 10.0
        p += 1
    # p could be >= 100 at this point, but we can't do anything
    return "{:.15f}E{:+04d}".format(n, p)

answered Sep 19 '18 at 13:23

khachik

28,112
9
59
94

Great! Thank you for the tip. Yes, it should also work for negative exponents as the first digit after the comma should always be non zero. I will add that to the function. Thank you! – N. Unger Sep 19 '18 at 13:38

score 0 · Answer 2 · answered Sep 19 '18 at 14:08

Some glorious hackery. Uses the usual Python scientific notation string formatting, then modifies the result by shifting all of the digits along by 1 and incrementing the exponent by 1.

import re

def sci_after_point(number, significant_digits=15, exponent_digits=3):
    '''Returns the number in scientific notation
    with the significant digits starting immediately after the decimal point.'''

    number_sci = f'{number:.{significant_digits-1}E}'

    sign, lead, point, decimals, E, exponent =\
    re.match(r'([-+]?)(\d)(\.)(\d+)(E)(.*)', number_sci).groups()

    incremented_exponent = int(exponent) + 1
    incremented_exponent = f"{incremented_exponent:+0{exponent_digits + 1}}"

    return sign + '0' + point + lead + decimals + E + incremented_exponent

sci_after_point(-0.313575791515242E005)
Out: '-0.313575791515242E+005'

Is there a string format for floats which always starts with 0.x?

2 Answers2