Change mantissa in scientific notation from 0-1 instead of 1-10

Question

I want to format a number so that the mantissa is between 0 and 1 instead of 1 and 10 in scientific notation.

For example;

a=7.365
print("{:.6e}".format(a))

This will output 7.365000e+00, but I want it to be 0.736500e+01.

Answer 1

I suppose you could always try constructing your own preformatted string. (No idea if this works in Python 2.7, though).

import math

def fixit( x, n ):
   if x == 0.0: return f" {x:.{n}e}"

   s = ' ' if x >= 0 else '-'
   y = math.log10( abs(x) )
   m = math.floor(y) + 1
   z = 10 ** ( y - m )
   return s + f"{z:.{n}f}e{m:+03d}"

for x in [ -7635, -763.5, -76.35, -7.635, -0.7635, -0.07635, -0.007635, 0.007635, 0.07635, 0.7635, 7.635, 76.35, 763.5, 7635 ]:
    print( fixit( x, 6 ) )
for x in [ -10, -1, -0.1, -0.01, 0.0, 0.01, 0.1, 1, 10 ]:
    print( fixit( x, 6 ) )

Output:

-0.763500e+04
-0.763500e+03
-0.763500e+02
-0.763500e+01
-0.763500e+00
-0.763500e-01
-0.763500e-02
 0.763500e-02
 0.763500e-01
 0.763500e+00
 0.763500e+01
 0.763500e+02
 0.763500e+03
 0.763500e+04
-0.100000e+02
-0.100000e+01
-0.100000e+00
-0.100000e-01
 0.000000e+00
 0.100000e-01
 0.100000e+00
 0.100000e+01
 0.100000e+02

Answer 2

You could do something like the following:

import math

x = 0.07365

def zero_one_mant(x):
    """
    Return a string for the input number `x`, where the mantissa is always
    between 0 and 1 and the exponent is adjusted accordingly.
    """

    exp = int(math.floor(math.log10(x))) + 1
    
    mant = x / 10**exp
    
    return "{0:.6f}e{1:+03d}".format(mant, exp)
    

for x in [0.07365, 7.365, 73.65]:
    print(zero_one_mant(x))

0.736500e-01
0.736500e01
0.736500e02