Compare strings using the `==` operator.
Compare strings using the `==` operator.

Checking for equal strings using `is` is not save. See https://stackoverflow.com/questions/2988017/string-comparison-in-python-is-vs

Or play around with:
```python
for i in xrange(10):
     print i, 'a'*i is 'a'*i
```
which gives me:
```
0 False
1 True
2 False
3 False
4 False
5 False
6 False
7 False
8 False
9 False
```
capaulson/pyKriging