NotImplementedError: 'AnnAssign' nodes are not implemented but numpy-like syntax works
My dataframe ``df`` has a column called "Unnamed:_6" which is of dtype ``object``.

Running the following command works just fine:
```python
df[df['Unnamed:_6'] == "Foo"]
```

However, the equivalent line:
```python
df.query('Unnamed:_6 == "Foo"')
```
raises the following exception:
```python
NotImplementedError: 'AnnAssign' nodes are not implemented
```
