[Python] How to add value from a list as new column value in dataframe, if existing column...

I have a dataframe which looks like shown below:

CALL_START IMSI
0 24.07.2025 12:00:51 123456888888888
1 24.07.2025 17:58:57 123456999999999
2 24.07.2025 17:05:47 543214511111111
3 24.07.2025 17:02:30 543214522222222
4 24.07.2025 16:07:44 987654444444444
5 24.07.2025 16:07:49 777777444444444


Dataframe has tens of thousands of rows and list used for comparing values is pretty short, lets say it has one hundred elements with different element length (5 or 6 characters) as shown below:

['123456', '54321', '98765']


I would like to check if values from IMSI column (which is an object type - str) startswith values from a list and if so to add new columns to dataframe, one having value from a list and other column as boolean value. Something like this:

CALL_START IMSI BAN FLAG
0 24.07.2025 12:00:51 123456888888888 123456 True
1 24.07.2025 17:58:57 123456999999999 123456 True
2 24.07.2025 17:05:47 543214511111111 54321 True
3 24.07.2025 17:02:30 543214522222222 54321 True
4 24.07.2025 16:07:44 987654444444444 98765 True
5 24.07.2025 16:07:49 777777444444444 None False


So if value from IMSI column starts with value from list, add that value to a dataframe and add True to new column FLAG, if value from IMSI column does not starts with any element from a list add None (or whatever, it can be empty string) and add False to FLAG

It is also acceptable to have only matches (without FLAG column):

CALL_START IMSI BAN
0 24.07.2025 12:00:51 123456888888888 123456
1 24.07.2025 17:58:57 123456999999999 123456
2 24.07.2025 17:05:47 543214511111111 54321
3 24.07.2025 17:02:30 543214522222222 54321
4 24.07.2025 16:07:44 987654444444444 98765


I know i can use pd.Series.str.startswith() but this approach returns only Series with True or False value.

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