How to evaluate a string and keep precision in Python

Question

I’m trying to get a more precise result from this code:

a = str(10**20+10**-20)
b = eval(a)

I want to obtain around 42 decimal places so Python doesn’t round it to 1e+20.

Possible duplicate of Limiting floats to two decimal points

henrywongkk
– henrywongkk

2019-10-04 01:54:57 +00:00
Commented Oct 4, 2019 at 1:54 — henrywongkk
– henrywongkk, Commented Oct 4, 2019 at 1:54

Michele Bastione · Accepted Answer · 2019-10-04 11:48:15Z

1

You actually 'only' need 41 to accomplish that. Use the decimal module:

import decimal
decimal.getcontext().prec=41
a = 10**20+10**decimal.Decimal(-20)

Python's floating-point types are just as inaccurate as in any other language. The decimal module contains the Decimal data structure, capable of handling arbitrarily long decimal numbers instead. You can read more about it here: check it out.

edited Oct 4, 2019 at 11:48

answered Oct 4, 2019 at 2:13

Michele Bastione

3633 silver badges13 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Shmack Over a year ago

Your comment on my post is correct. I removed it to deter potential confusion and upvoted yours.

Collectives™ on Stack Overflow

How to evaluate a string and keep precision in Python

1 Answer 1

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related