Slow autocompletion in python/ipython console for large DataFrame containing strings
I'm not sure if this is the right place to ask, but it seems the autocompletion in python or ipython console is especially slow for large DataFrame with strings (object) in it.

For example, consider the following two DataFrames:

```python
import numpy as np
import pandas as pd
df1 = pd.DataFrame(np.random.rand(400000,60))
df2 = pd.DataFrame([["asdfasdf"]*60]*400000)
```

By typing `df1.<TAB>` in the interactive python/ipython session, the autocompletion is quick, but it takes a very long time for `df2.<TAB>` to finish (it gets stucked for many seconds).

I'm not sure if this is due to different implementation of pandas for DataFrames containing numbers vs. strings (object), or this is due to issues in the interactive python/ipython session.
