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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 current_codes_from_pdb():
 """ Get list of all PDB codes currently listed in the PDB. Returns ------- pdb_codes : list(str) List of PDB codes (in lower case). """

    url = 'http://www.rcsb.org/pdb/rest/getCurrent'
    r = requests.get(url)
    if r.status_code == 200:
        pdb_codes = [x.lower() for x in r.text.split('"') if len(x) == 4]
    else:
        print('Request for {0} failed with status code {1}'.format(url, r.status_code))
        return
    return pdb_codes