@SkiNoCap in the settings menu, keyboard and indentation, you can control whether pythonista uses tabs or spaces when hit tab, and whether to use 3 or 4 spaces.
Tabs are good for retaining semantic meaning, but not great for actually formatting with a specific format in mind. In other words, tabs are good for storing data, but usually not for display.
The idea of tabs for indentation is good -- similar to the way xml allows for device independent storing of data, which can then be rendered in a way that makes sense (say, small devices could use smaller spaces, or formatting into tabular format, etc)
But the reality is that many editors don't properly support tabs, and it is usually hard to tell the difference between spaces and tabs, so your safest bet is to set pythonista to replace tabs with 3 or 4 spaces depending on your aesthetic.