import re


def get_filename_from_cd(cd):
    """
    Get the filename from content disposition
    
    Parameters:
        cd : content disposition (from https://www.w3.org/Protocols/
            rfc2616/rfc2616-sec19.html). The Content-Disposition 
            response-header field has been proposed as a means for 
            the origin server to suggest a default filename if the 
            user requests that the content is saved to a file. 
            This usage is derived from the definition of 
            Content-Disposition in RFC 1806 [35].

    Returns:
        The filename from content disposition (cd)
    """
    if not cd:
        return None
    fname = re.findall('filename=(.+)', cd)
    if len(fname) == 0:
        return None
    return fname[0][2:-1]