[ide] Does Notepad++ show all hidden characters?

In Notepad++ I have set "replace tab with 2 spaces".

When coding in Python I copy-pasted some code from the web and it appeared indented correctly. But running the code resulted in indentation errors, which I solved in the end by removing all "visible" spaces at line beginnings and inserting the same amount of spaces again.

Could it be possible that Scintilla based Notepad++ does not show all special characters, but displays them as spaces? Is there a setting to fix this?

Yes, and unfortunately you cannot turn them off, or any other special characters. The options under \View\Show Symbols only turns on or off things like tabs, spaces, EOL, etc. So if you want to read some obscure coding with text in it - you actually need to look elsewhere. I also looked at changing the coding, ASCII is not listed, and that would not make the mess invisible anyway.

In newer versions of Notepad++ (currently 5.9), this option is under:

View->Show Symbol->Show All Characters

or

View->Show Symbol->Show White Space and Tab

Double check your text with the Hex Editor Plug-in. In your case there may have been some control characters which have crept into your text. Usually you'll look at the white-space, and it will say 32 32 32 32, or for Unicode 32 00 32 00 32 00 32 00. You may find the problem this way, providing there isn't masses of code.

Download the Hex Plugin from here; http://sourceforge.net/projects/npp-plugins/files/Hex%20Editor/

For non-printing characters, you can do the following:

• if you could identify the character, where cursor takes 2 arrow keys to move, just select that character.
• do Ctrl-F
• now you can count or replace or even mark all such characters