Pandas: extract hour from timedelta

Divide by np.timedelta64(1, 'h'):

df1['B'] = df1['A'] / np.timedelta64(1, 'h')
print (df1)
         A    B
0 02:00:00  2.0
1 01:00:00  1.0
2 02:00:00  2.0
3 03:00:00  3.0

You can use dt.components and access the hours column:

In[7]:
df['B'] = df['A'].dt.components['hours']
df

Out[7]: 
         A  B
0 02:00:00  2
1 01:00:00  1
2 02:00:00  2
3 03:00:00  3

the timedelta components returns each component as a column:

In[8]:
df['A'].dt.components

Out[8]: 
   days  hours  minutes  seconds  milliseconds  microseconds  nanoseconds
0     0      2        0        0             0             0            0
1     0      1        0        0             0             0            0
2     0      2        0        0             0             0            0
3     0      3        0        0             0             0            0