Pressing <Tab> while the cursor is in a string will bring up the file completion dialog rather than inserting a tab (or 4 spaces). This behavior is rather annoying in a text editor especially when editing multiline doc strings.
This behavior is new to the 3.3 series as a consequence of issue14937. Arguably, it is a regression.
The logic for bringing up the file completion window when pressing Tab in a string needs to be revised. If the string already contains a partial match, then bring up the window when pressing Tab, otherwise insert a Tab character or spaces.
Alternatively, the Ctrl+Space key sequence will already bring up the file completion dialog, so having an automatic Tab completion behavior is not absolutely necessary.
This issue can also be triggered in the shell. Start a string and then press tab twice.