### Sage is not preparsing Python 3 integers

Hello, Sage community!

With the upcoming migration of Sage from Python 2 to Python 3 (really soon, let us hope!), there are some testings I have been trying, and I have noticed that the "underscored integer literals", like "1_000_000" are not preparsed by Sage. For example,

```
preparse('1_000_000 + 3')
```

results in

```
'1_000_000 + Integer(3)'
```

However,

```
preparse('1000000 + 3')
```

returns

```
'Integer(1000000) + Integer(3)'
```

On the other hand, if I write

```
type(1_000_000 + 3)
```

the result is

```
<class 'sage.rings.integer.Integer'>
```

which is great, but

```
type(1_000_000 + 3_000)
```

instead gives me

```
<class 'int'>
```

Finally,

```
type(1000000 + 3000)
```

gives us

```
<class 'sage.rings.integer.Integer'>
```

I know one of the reasons for the `Integer`

type was to allow divisions like `3/2`

to return the float ~~1.5 ~~`1.5`

even with Python 2, which would return (very disturbingly) ~~1, ~~`1`

, in other case. However, Python 3 integers already do this. Besides what I ~~mentioned, ~~mentioned above and this, I haven't found any other difference in behavior.

So I was wondering: Is there any disadvantage in Sage not being preparsing this type of literals?