Bitcoin Core – Understanding numeric encoding in scripts, CScriptNum

What is a brief explanation of CScriptNum, the numeric encoding used for arithmetic opcodes in Bitcoin Script?

What would an illustrative pseudocode/Python example look like?

What should be the encoding of the following decimal point (hexadecimal)?

• 42
• 88
• 257
• 17000
• 8589934592

When is it not 4 bytes?

See also:

Why are arithmetic script opcodes limited to 4-byte operands?

Bitcoin arithmetic operations (OP_ADD, etc.)

compressed integer in script