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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 _parse_pem_data(pem_data):
 """Parse PEM-encoded X.509 certificate chain. Args: pem_data: str. PEM file retrieved from SignatureCertChainUrl. Returns: list or bool: If url is valid, returns the certificate chain as a list of cryptography.hazmat.backends.openssl.x509._Certificate certificates where certs[0] is the first certificate in the file; if url is invalid, returns False. """

    sep = '-----BEGIN CERTIFICATE-----'
    cert_chain = [six.b(sep + s) for s in pem_data.split(sep)[1:]]
    certs = []
    load_cert = x509.load_pem_x509_certificate
    for cert in cert_chain:
        try:
            certs.append(load_cert(cert, default_backend()))
        except ValueError:
            warnings.warn('Certificate is invalid.')
            return False

    return certs