def is_exon(string):
    """Does the string contains 'exon' preceded or not by spaces.

    :param string: The string to be tested.

    :Example:

    >>> from pygtftk.utils import is_exon
    >>> assert is_exon("Exon") and is_exon("exon")

    """
    if string.lower().strip() == 'exon':
        return True
    return False
