def to_underscore(string):
new_string = re.sub(r'<STR_LIT>', r'<STR_LIT>', string)<EOL>new_string = re.sub(r'<STR_LIT>', r'<STR_LIT>', new_string)<EOL>return new_string.lower()<EOL>
Converts a given string from CamelCase to under_score.

    >>> to_underscore('FooBar')
    'foo_bar'