How to write a number in scientific notation in Python keeping the mantissa as integer

Question

Suppose I have x=3.141516 and y=0.00129. I need to format those numbers in scientific notation but the mantissa must not have decimal places. For example:

x = 3141516e-6
y = 129e-5

I have no idea how to solve this, since formatting in Python looks always assume decimal places.

Answer 1

I'm not aware how you can do it with str.format (to not have any decimal places), but you can construct the string manually (with help of decimal module):

import decimal


def get_num(x):
    t = decimal.Decimal(str(x)).as_tuple()
    return f'{"-" if t.sign else ""}{"".join(map(str, t.digits))}e{t.exponent}'


print(get_num(3.141516))
print(get_num(0.00129))
print(get_num(-1.23))

Prints:

3141516e-6
129e-5
-123e-2