import re

data1 = "aaab"
data2 = "aaaba"
data3 = "bbba"
pattern = r'a+b'

b1 = re.match(pattern, data1)
# b1 is <...span=(0, 4), match='aaab'>

b2 = re.match(pattern, data2)
# b2 is <...span=(0, 4), match='aaab'>

b3 = re.match(pattern, data3)
# b2 is None

print(f"{b1 = }")
print(f"{b2 = }")
print(f"{b3 = }")