convert number to scientific notation python with a variable

Question

I want to use str.format to convert 2 number to scientific notation raised to the same exponential but the exponential need to be set off the str.format. Example:

from math import log10 y=10000 x=round(np.log10(y)) m=10 y="{:e}".format(y) m="{:e}".format(m) print(y) print(m)

here I have that m has e = 1 and y e = 4 and what I want is for both to have the same "e". i want to set both to exponencial x.

@samcarter_is_at_topanswers.xyz oh man, really thx xD I put the aswer at my post, but if u want put yourself I will give u right — Miguel
– Miguel, Commented Mar 15, 2021 at 16:45

luuk · Accepted Answer · 2020-12-21 20:35:08Z

I think you have to calculate this yourself, for example using a helper function which returns a string:

def format_exp(x, n): significand = x / 10 ** n exp_sign = '+' if n >= 0 else '-' return f'{significand:f}e{exp_sign}{n:02d}'

Explanation:

x is the number to format, and n is the power that you want to display;
significand calculates the part to show in front of the e by dividing x by 10ⁿ (10 ** n);
exp_sign is either + or -, depending on the value of n (to replicate the default behaviour).

Example usage:

>>> import math >>> y = 10000 >>> m = 10 >>> x = math.floor(math.log10(y)) # x = 4 >>> print(format_exp(y, x)) 1.000000e+04 >>> print(format_exp(m, x)) 0.001000e+04 >>> print(format_exp(y, 1)) 1000.000000e+01 >>> print(format_exp(m, 1)) 1.000000e+01

You can increase the complexity of this function by adding an additional parameter d to set the number of decimals printed in the significand part (with a default value of 6 to reproduce the default Python behaviour):

def format_exp(x, n, d=6): significand = x / 10 ** n exp_sign = '+' if n >= 0 else '-' return f'{significand:.{d}f}e{exp_sign}{n:02d}'

With this function, you can control the number of decimals printed:

>>> print(format_exp(y, x)) # default behaviour still works 1.000000e+04 >>> print(format_exp(y, x, 4)) 1.0000e+04 >>> print(format_exp(y, x, 1)) 1.0e+04

i can solve that way as well, but I wanted to know if it's possible like i wanted. I will wait a bit more, if not i'm going accpet your answer as corret.
@MiguelGodinho The Format String Syntax section of the Python documentation does not mention any possibility of choosing the exponent using the built-in format function; the only digits you can enter are width (total width of the formatted string, filled with spaces or any other desired character) and precision (number of digits after the decimal point).
I was trying to change precision, maybe another library has what I want
@MiguelGodinho What do you mean by changing precision? The function format_exp can be expanded with some additional mathematics if you want to specify the number of significant digits instead of the number of decimals printed.
I wanted to say another thing but nvm. I can't find another answer, going to give yours, right.

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