Option #1 - Show All Characters

You can download Notepad++ and open the file there. Then, go to the menu and select View->Show Symbol->Show All Characters. All characters will become visible, but you will have to scroll through the whole file to see which character needs to be removed.

Unfortunately, Notepad++ will automatically convert line endings according to your Edit->EOL Conversion selection, so it won't help if your non-printable characters are CR or LF.

Option #2 - TextFX Zap Non-printable Chars

Alternatively, you could install the TextFX plugin from SourceForge, and use TextFX->TextFX Characters->Zap all non-printable characters to #. This will replace some non-printable characters with a pound sign, but not CR or LF.

Option #3 - Remove BOM Encoding

Lastly, you could use Notepad++, and use Encoding->Convert to UTF8 without BOM. This will remove non-printable characters which occasionally causes issues with certain renderers (VSO).

I don't know of any built-in method, but it's fairly easy to do using a comprehension:

import string
printable = string.ascii_letters + string.digits + string.punctuation + ' '
def hex_escape(s):
    return ''.join(c if c in printable else r'\x{0:02x}'.format(ord(c)) for c in s)

You could do the comparison of the bytes by storing the strings as constants, with decent names. So case "\0\0": would become case STATUS_CRYPTO_1: which helps remove the 'magic number' aspect of your switch statement.

But the correct solution here is to add some comments. That's what comments were designed for, that's their intended purpose. Some documentation at the top of your function is probably the best place to say what the byte array is that you're comparing against, and why.

The graphic characters would be the one for which the isgraph()/iswgraph() standard functions return true or the ones matched by the [[:graph:]] regular expressions, that is the ones in the graph character class in the locale.

Per POSIX, the print class must be a superset of graph and be disjunct from cntrl and graph must be a superset of upper, lower, alpha, digit, xdigit, and punct and must not include the space (U+0020) character (with no mention of other whitespace characters).

The idea being that the graphic characters would be the ones for which ink would be used to draw them, while printable would be the non-control ones.

In practice, on GNU systems (such as Ubuntu) at least print is graph plus the non-control characters from the space class. Here with glibc 2.35 (as used on Ubuntu 22.04) and in UTF-8 locales, that includes:

U+0020 SPACE
U+1680 OGHAM SPACE MARK
U+2000 EN QUAD
U+2001 EM QUAD
U+2002 EN SPACE
U+2003 EM SPACE
U+2004 THREE-PER-EM SPACE
U+2005 FOUR-PER-EM SPACE
U+2006 SIX-PER-EM SPACE
U+2008 PUNCTUATION SPACE
U+2009 THIN SPACE
U+200A HAIR SPACE
U+205F MEDIUM MATHEMATICAL SPACE
U+3000 IDEOGRAPHIC SPACE

While the space class has:

U+0009 CHARACTER TABULATION
U+000A LINE FEED
U+000B LINE TABULATION
U+000C FORM FEED
U+000D CARRIAGE RETURN
U+0020 SPACE
U+1680 OGHAM SPACE MARK
U+2000 EN QUAD
U+2001 EM QUAD
U+2002 EN SPACE
U+2003 EM SPACE
U+2004 THREE-PER-EM SPACE
U+2005 FOUR-PER-EM SPACE
U+2006 SIX-PER-EM SPACE
U+2008 PUNCTUATION SPACE
U+2009 THIN SPACE
U+200A HAIR SPACE
U+2028 LINE SEPARATOR
U+2029 PARAGRAPH SEPARATOR
U+205F MEDIUM MATHEMATICAL SPACE
U+3000 IDEOGRAPHIC SPACE