import re

contents = [
    "AB23",
    "A2B3", 
    "DE09",
    "MN90",
    "XYi9",
    "XY90"
]

for content in contents:
    regex_pattern = "(?:AB|DE|XY)\d+" 
    # starts with AB or DE; should contain one or more number

    m = re.match(regex_pattern, content)

    if(m):
        print('matched : '+content)

matched : AB23
matched : DE09
matched : XY90