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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def is_hex_string(string):
 """Check if the string is only composed of hex characters."""

    pattern = re.compile(r'[A-Fa-f0-9]+')
    if isinstance(string, six.binary_type):
        string = str(string)
    return pattern.match(string) is not None