BUG: Allow typecode of 'e' to be passed to select_dtypes
Closes #11990.

hmm why does his raise a TypeError? float16 is platform specific I think ?
 np.e is defined and it's a float :)

```
In [1]: np.e
Out[1]: 2.718281828459045
```
 add a whatsnew note as well
 minor change, pls squash, ping when green.
 can you update
 Green.
 I find your patch fine. But isn't this odd?

```
In [11]: df = DataFrame(np.random.randn(10,2))

In [12]: df[0] = df[0].astype('float16')

In [13]: df.dtypes
Out[13]: 
0    float16
1    float64
dtype: object

In [14]: df.select_dtypes(include=['float'])
Out[14]: 
          1
0 -0.458946
1  0.456845
2  1.246123
3  1.296991
4  1.445800
5  1.082351
6 -0.895652
7  0.031383
8  1.320909
9 -1.783126

In [15]: df.select_dtypes(include=['float16'])
Out[15]: 
          0
0 -0.501465
1  0.623047
2  0.207397
3 -0.251465
4  1.599609
5 -2.359375
6  0.354004
7 -0.191650
8 -1.067383
9 -0.903320
```
 merged via https://github.com/pydata/pandas/commit/138b8ba853a6f4356b23d37d76e69425373f3315
 That would be my expectation since `np.float64 == np.dtype(float)`, platform dependent. It's one of the reasons I ran into this, trying to use all float types to capture all eventualities. 
 Actually, it might be nice to just accept the all typecode aliases too.

On Tue, Jan 12, 2016, 5:48 PM Jeff Reback notifications@github.com wrote:

> Closed #11991 https://github.com/pydata/pandas/pull/11991.
> 
> —
> Reply to this email directly or view it on GitHub
> https://github.com/pydata/pandas/pull/11991#event-513097549.
 would accept PR for that addition
