I don't have a Mac and use UltraEdit only on Windows on which I don't use Samba. I cannot really help for that reason with information what to change in configuration of UltraEdit for Mac or of Samba. I know from other forums posts that UltraEdit users edit files on Raspberry Pi using FTP or SFTP, the latter often with a private/public key pair.

There are several configuration settings in UltraEdit for Windows which control how UltraEdit is updating an existing file on save. These options are in configuration at File handling - Advanced and are described on UltraEdit Wiki page Settings:File handling:Advanced. Please note that some of the settings described on this page do not exist anymore in currently latest version of UltraEdit for Windows. I am quite sure that some of these settings do also not exist in UltraEdit for Mac.

Here is a list of forum topics containing the word Samba:

• UltraEdit + Samba - on save : "File changed, reload file?"
• Auto File Change Detection on Files in a Project
• Enforce specific encoding
• Case-sensitive filenames on Unix drives mounted on Windows using Samba
• Explorer performance over samba
• *NIX File Permissions

I cannot answer your new question as I use Windows and not Linux or Mac. Python script files are usually small files with less than 1 MB. The update of a small file on file save should be done within one or two seconds in the file system on Raspberry Pi. There is definitely something not correct configured either in UltraEdit for file save on Samba mounted file system or in the Samba configuration settings on Mac or on Raspberry Pi. Well, the configuration on Raspberry Pi can be more or less excluded as possible cause of the delay because of the file busy issue cannot be reproduced on using other text editors on Mac according to your problem description. It is more likely an issue caused by how UltraEdit for Mac makes a file save (with backup feature enabled) and how Samba handles that file save process.