I'm trying to find the starting position of a string in an URL contained in column['url'] if column ['Existe'] contains "F" or "D". I'm new to Python and I'm trying to replicate a workflow from Excel in Python and after an hour of trying methods with lambda, numpy.where or numpy.select, and searching the web, I had to ask for help.

I've tried applying the following code, but this only returns that the value exists, but doesn't actually gives me the position in the string. What I currently have is:

```
df['Start']= ["/t/" in x[0] and "F" in x[1] for x in zip(df['url'],df['Existe'])]

```

Basically, the results it gives me is the following:

```
       order     id       date      time  URL                    typedCount transition  Existe  Start
0          0  14438   1/3/2021  14:49:37  messenger.com/t/xxxxx          0       link       F   True
1          1  14437   1/3/2021  14:49:18  messenger.com/t/xxxxx          0       link       F   True

```

What I'm trying to do is to find the starting position of "/t/" in df['url'] if "F" exists in df['Existe'] and placing the result in a new column, df['Start']. I have to use this conditional because df['Existe'] contains both "F" and "D", and it has to look for "/t/" if it's "F", and "/@me/" if it's "D".

The result I'm looking for is:

```
       order     id       date      time  URL                    typedCount transition  Existe  Start
0          0  14438   1/3/2021  14:49:37  messenger.com/t/xxxxx          0       link       F   14
1          1  14437   1/3/2021  14:49:18  messenger.com/t/xxxxx          0       link       F   14

```

Does anyone know a way of doing this?

Thanks