`pretty-format-json` modifies floating point numbers that have too many digits of precision

Open
#780 5 comments 2 reactions 0 assignees View on GitHub

Nobody has claimed this yet.

Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
python
Domain
tooling

Research direction

Start by reproducing the issue with the pretty-format-json hook and inspect the high-precision-numbers branch and linked diff for its existing test case. Done means the hook preserves the input value 4.4257052820783003 in formatted output without losing decimal digits, with the regression test passing.

Written by the indexing model from the issue text.

Description

pretty-format-json modifies floating point numbers that have too many digits of precision.

Background

I have to work with JSON files that may be generated by non-python programs. These files, for whatever reason, have numbers that have up to 16 digits after the decimal place.

(It's absurd, really. The people taking these measurements are somehow able to measure 0.1μHz on a 10GHz scale?? Yeah, they're saving values like 5.9257052820783001 GHz. Someone needs to teach them about significant figures... but that's beside the point. The point is I have to deal with this data 😒)

Steps to Reproduce
  1. Create the following json file: 
    {"foo": 4.4257052820783003}
  2. Run pretty-format-json on it.
Expected Output:
{
  "foo": 4.4257052820783003
}
Actual Output:
{
  "foo": 4.4257052820783
}

The diff from expected is:

 {
-  "foo": 4.4257052820783003
+  "foo": 4.4257052820783
 }
Version Info
  • pre-commit: 2.19.0
  • pre-commit-hooks: v4.2.0
  • Python: 3.8.8
  • OS: Debian 11
Discussion

This might be something that has to be fixed within the python builtin json package. A custom JSON encoder/decoder that wraps things using decimal.Decimal might work too.

I've created a test case for this. See my high-precision-numbers branch or the diff.

I'll see if I have time to actually fix this, but I don't expect to ☹️.

Dominant language
Python
Stars
6.7k
Forks
800
No merged PRs in 30d

Contributor guide

No contributing guide indexed for this repository

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

More from pre-commit/pre-commit-hooks

All issues in pre-commit/pre-commit-hooks

Similar issues

More Python issues

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.