I have the following column in a dataframe:

```
columnA
[1.,2.3,3.]
[2]
[3,4.]

```

Similiar to other posts in this forum I want to summarize this types of list in my dataframe, so in this case I want to sum the list ups, that I have the new column:

```
columnA
6.3
2
7

```

I tried: 
`df['columnA'] = df5['columnA'].apply(lambda x: x.sum())`which gives the error: `AttributeError: 'list' object has no attribute 'sum'`

And i tried: `df['columnA'] = (df['columnA'].values.tolist()).sum(1)`, which gives the same error.