I'm trying to extract the hour from the entire data+time column df['Start Time']. Is there any easy way to do that using str.extract()? Any support is appreciated!!

```
    Start Time             
2019-01-14 07:42:00    
2019-01-14 05:29:00    
2019-01-14 08:01:00    
2019-01-18 04:20:00  
2019-01-14 05:30:00   
       ... 
2018-04-09 10:15:33   
2018-12-14 06:36:46     
2018-04-11 07:51:24    

```

I've tried:

```
df['Start Hour'] = df['Start Time'].str.split(' ', 1)

```

Output

```
    Start Time             
2019-01-14   
2019-01-14  
2019-01-14    
2019-01-18  
2019-01-14  
       ... 
2018-04-09    
2018-12-14    
2018-04-11 

```

Desired Output

```
    Start Time             
07
05 
08  
04
05
   ... 
10
06  
07

```