BUG: Fix astype from float32 to string

[dsaxton]

• closes BUG: conversion of float32 to string shows too much precision #36451
• tests added / passed
• passes black pandas
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

It seems both bugs were caused by the same behavior from numpy:

[ins] In [1]: import numpy as np

[ins] In [2]: arr = np.array([0.1], dtype=np.float32)

[ins] In [3]: arr
Out[3]: array([0.1], dtype=float32)

[ins] In [4]: np.asarray(arr, dtype="object")
Out[4]: array([0.10000000149011612], dtype=object)

[jorisvandenbossche]

Thanks for the catch and quick fix!

(so it's actually not numpy, but stdlib float that has the different behaviour)

[jreback]

if you can update the whatsnew

[jorisvandenbossche]

Thanks @dsaxton !

[jorisvandenbossche]

@meeseeksdev backport to 1.1.x

[lumberbot-app]

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

$ git checkout 1.1.x
$ git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

$ git cherry-pick -m1 a0d6d061de42c54b8071d28a4bf60cd69853c388

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

$ git commit -am 'Backport PR #36464: BUG: Fix astype from float32 to string'

4. Push to a named branch :

git push YOURFORK 1.1.x:auto-backport-of-pr-36464-on-1.1.x

5. Create a PR against branch 1.1.x, I would have named this PR:

"Backport PR #36464 on branch 1.1.x"

And apply the correct labels and milestones.

Congratulation you did some good work ! Hopefully your backport PR will be tested by the continuous integration and merged soon!

If these instruction are inaccurate, feel free to suggest an improvement.