I want to extract a character before and after certain characters in a string, most of these are in a pandas dataframe column.

Basically I want to take from my principal dataframe and merge together is from my columns 'Strain' and 'Region' taking the following items:

i) Original Strain: Streptomyces_sp_QL40_O

ii) Original Region: Region&nbsp1.1

Extract:

1. The string after the second underscore Ex: QL40
2. The first number before the '.' Ex: nbsp.1
3. The second number after the '.' Ex: .1
4. The string region before the '&' character
5. Finally to add two 0's after string 'region' if digit is less than 10 and one 0 if digit is more than ten.

Desired Output: QL40_1.region001

I am almost there but can't place the 0's after the region and before the last number.

Here is a snippet of my code if anyone has any idea on what I might be doing incorrectly?

def modify_dataframe(df_rows):
regions = []
for i in df_rows['Region'].str.split('.').str[0]:
    regions.append(''.join([d for d in i if d.isdigit()]))  
df_rows['BGC Region'] = df_rows['Strain'].str.split('_').str[2] + '_' + regions + '.region'
print (df_rows)
region_number = df_rows['Region'].str.split('.').str[1]
for i, rn in enumerate(region_number):
    if int(rn) < 10:
        df_rows['BGC Region'][i] += '00' + rn
    elif int(rn) < 100:
        df_rows['BGC Region'][i] += '0' + rn
return df_rows