Improve readability of the predict script

[tfujiwar]

What this patch does to fix the issue.

This script was reviewed by a readability reviewer before but was not fixed yet.
#838 (review)

Link to any relevant issues or pull requests.

Closes #868 .

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• Readability Approval for Python from tkng, tsawada

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[iizukak]

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[tsawada]

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[tfujiwar]

/ready

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