ValueError when use multi-conditions inquiry
I want to use pandas to retrieve data with multi-conditions, but now I only use:
```python
import pandas as pd
import numpy as np

df = pd.DataFrame({'a':[9,2,3,4,1,6],'b':[5,6,1,8,3,9]})
s = np.percentile(df.a,(25,75))
df[(df.a>s[0]) & (df.a<s[1])]
```
My question is: I can only use `df[(df.a>s[0]) & (df.a<s[1])]` to retrieve data, but I can't use `df[df.a>s[0] and df.a<s[1]]` to retrieve data. When I use `df[df.a>a[0] and df.a<a[1]]`, it shows: `ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().`. 

