Here's what I wrote originally, and it worked.
pyg = "ay"
original = raw_input("Enter what you want to drink now")
if len(original) > 0 and original.isalpha():
first_letter = original
new_word = original[1:len(original)]
print new_word + first_letter + pyg
But I found that originally it has to be like below.
word = original.lower()
first_letter = word 
why it should be ".lower()"?