develop: improve python mysqlclient sample code doc

[Mini256]

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• This PR is translated from: develop: refactor Python mysqlclient tutorial docs#14544
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[Oreoxmt]

@Mini256 Mini256#1 PTAL

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[Oreoxmt]

Rest LGTM

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-08-29 07:40:54.196809276 +0000 UTC m=+1826418.745825262: ☑️ agreed by ran-huang.
• 2023-08-31 07:42:44.268999176 +0000 UTC m=+1999328.818015162: ☑️ agreed by Oreoxmt.

[Oreoxmt]

/approve

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Oreoxmt

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #14941.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #14942.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.2: #14943.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.3: #14944.