BUG: float truncation in eval with py 2
- [x] closes #14241
- [x] tests added / passed
- [x] passes `git diff upstream/master | flake8 --diff`
- [x] whatsnew entry

Python 2 only - apparently `str()` rounds shorter than `repr()`

```
In [1]: f = 1000000000.006

In [2]: str(f)
Out[2]: '1000000000.01'

In [3]: repr(f)
Out[3]: '1000000000.006'
```
