将科学计数法中的浮点数转换为“d.dd x 10^(-n)”

Question

I'm building a calculator to calculate some chemistry related calculations. So most of the results will be extremely small values.

An example result is 4.840909814726882e-09 .

How do I display this value in a format like 4.84 x 10^(-9) ?

Answer 1

try this:

format(4.840909814726882e-09, '.2e').replace('e', ' x 10^(') + ')'

Output:
4.84 x 10^(-09)
It's not exactly the result you wanted but it's simple.

Also there is:

def my_format(num):
    s = format(num, '.2e')
    base, exp = s.split('e')
    return f'{base} x 10^({int(exp)})'

Output:

>>> my_format(4.840909814726882e-09)
'4.84 x 10^(-9)'

which is more coplicated but it's exectly the result you wanted.

Answer 2

How do I display the value to a format like 4.84 x 10^(-9)?

By hand, that is not a format supported by Python.

Although if you just want to "round off" the number because you neither have nor need 15 significant digits, then you can use format specifiers , and either the g presentation type:

>>> format(v, 'g')
'4.84091e-09'

or an explicit precision:

>>> format(v, '.3')
'4.84e-09'