import re
strings = [
"day__",
"day_"
]
pattern = "[a-zA-Z]_$"
for s in strings:
print(re.search(pattern, s))
aW1wb3J0IHJlCgpzdHJpbmdzID0gWwoJImRheV9fIiwKCSJkYXlfIgpdCgpwYXR0ZXJuID0gIlthLXpBLVpdXyQiCgpmb3IgcyBpbiBzdHJpbmdzOgoJcHJpbnQocmUuc2VhcmNoKHBhdHRlcm4sIHMpKQoKCg==