Basically I have following strings and I want to grab a sub-string from them.
input: RT4_MANGO_AF
output: MANGO
input:  RT4_DF5_WE_APPLE_AF 
output: APPLE 
input: TF_WE_BANANA_AF
output: BANANA
input: RT4_DF5_ORANGE_AF
output: ORANGE
Note the hint here is that, the last 3 chars will remain _AF and I want to grab the sub-string before  _AF and after the last-but-one _ symbol.
I have the following code which does the same, but I feel it's not optimal. Is there a way to optimize this code? or can I get optimized code?
sd = 'ER5_WE_APPLE_AF'
m = sd[:-3]
for i in range(len(m)):
    if m[i] == "_":
        si = i
    else:
        continue
m = m[si+1:]
print(m)
 
     
    