I have a pandas data frame with multiple columns. I want to create a new column `weighted_sum` from the values in the row and another column vector dataframe `weight` 

`weighted_sum` should have the following value:

`row[weighted_sum] = row[col0]*weight[0] + row[col1]*weight[1] + row[col2]*weight[2] + ...`

I found the function `sum(axis=1)`, but it doesn't let me multiply with `weight`.

Edit:
I changed things a bit.

`weight` looks like this:

```
     0
col1 0.5
col2 0.3
col3 0.2

```

`df` looks like this:

```
col1 col2 col3
1.0  2.2  3.5
6.1  0.4  1.2

```

`df*weight` returns a dataframe full of `Nan` values.