Following code using default credit card dataset:
```
import h2o
h2o.init(port=13334)
df = h2o.import_file("CreditCard_Cat-train.csv")
dropped = ["PAY_0"]
print(dropped)
df.drop(dropped)
print(dropped)
```
has following output:
```
['PAY_0']
[-7]
```
which shows that the variable `dropped` has change after the `df.drop` call from `['PAY_0']` to `[-7]`.
This means that user can not call `drop` on multiple frames in a row with the same input variable.
Duplicate of