Get number of digits after the dot in Float

[Paul Royik]

Rational(1,2).evalf(), how do I get 1 here (since 0.5 has 1 digit after the dot)?

[Aaron Meurer]

How would you count small numbers like 1.1e-30. Is that 1 digit or 31
digits after the decimal?

Aaron Meurer

On Thu, Apr 15, 2021 at 2:31 PM Paul Royik <distan...@gmail.com> wrote:
>
> Rational(1,2).evalf(), how do I get 1 here (since 0.5 has 1 digit after the dot)?
>

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[Paul Royik]

One digit. Ignore scientific notation.

[Aaron Meurer]

In that case, I think the simplest option would be to parse
str(float). Some split() and strip() operations should get you want
you want, or just use a regex.

Aaron Meurer

> To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/643b8e44-91f1-475f-87ed-f444d584bbaen%40googlegroups.com.

[Paul Royik]

How do I make sure that str() doesn't return exponential notation?

[Chris Smith]

>>> ndec = lambda x: 0 if '.' not in str(x) else len(str(x).split('.')[1].split('e')[0])

>>> (1, 1.0, 1.23, 1.234e-5, 3e5, 3e33)

(1, 1.0, 1.23, 1.234e-05, 300000.0, 3e+33)

>>> [ndec(i) for i in _]

[0, 1, 2, 3, 1, 0]

(Note that this is not the same thing as the number of significant digits. And if you don't want to count trailing 0s then change `[0]` to `[0].rstrip('0')`)

/c

[Paul Royik]

Thank you!