How to split string

[SriRajesh]

Hi,

I have below dataFrame and I want search and take the numeric value left side to specified substring.

My data:

df2 = pd.DataFramedf = pd.DataFrame({'ids': ['AA-120amp', 'BA+250A-52amp', 'AA-5623amp','CD']})

df2[['df2','rank']] = df2['ids'].str.split('-',expand=True)

print (df2: (output)
            ids      df2   allele     rank
0      AA-120amp       AA   120amp   120amp
1  BA+250A-52amp  BA+250A    52amp    52amp
2     AA-5623amp       AA  5623amp  5623amp
3             CD       CD     None     None

my desired output is:

            ids      df2   allele     rank
0      AA-120amp       AA   120amp   120
1  BA+250A-52amp  BA+250A    52amp   52
2     AA-5623amp       AA  5623amp   5623

I want to split the column at amp, and print numerical value left side to amp. If no amp exists in any row, just print None.
I tried above, but I could not be able to get in a single line what I want.