Local variable might be referenced before assignment

Question

This working function will receive a dictionary that will proceed with uploading or download files based on the transfer_type value. But currently my IDE is displaying the warning Local variable might be referenced before assignment when i'm using it to execute the subprocess.run stage.

My question is, should i accept the sugestion of declating as a global variable inside the function ( global cmd ) or should I ignore this suggestion?

def scp_transfer(data):

    host = data['host']
    remote = data['remote']
    local = data['local']
    transfer_type = data['transfer_type']

    if transfer_type == 'download':
        cmd = 'scp -qr %s:%s %s' % (host, remote, local)
    if transfer_type == 'upload':
        cmd = 'scp -qr %s %s:%s' % (local, host, remote)

    run = subprocess.run(cmd, shell=True, stdout=subprocess.PIPE)
    try:
        run.check_returncode()
    except subprocess.CalledProcessError as e:
        print(e.output)
    else:
        print(run.stdout.decode('utf-8'))

Answer 1

I would avoid declaring it as a global . You could declare it within the function:

cmd = None
if transfer_type == 'download':
    cmd = 'scp -qr %s:%s %s' % (host, remote, local)
if transfer_type == 'upload':
    cmd = 'scp -qr %s %s:%s' % (local, host, remote)

This could still cause issues when you try to run the cmd though. Instead, you should raise an exception if transfer_type doesn't match anything.

if transfer_type == 'download':
    cmd = 'scp -qr %s:%s %s' % (host, remote, local)
elif transfer_type == 'upload':
    cmd = 'scp -qr %s %s:%s' % (local, host, remote)
else:
    raise ValueError('Unexpected transfer type: %s' % transfer_type)

In any case, I would always pay attention to the warning.