python - OR operator inside OR operator - RegEX -

i'm trying create compiler in python , i'm using re module create tokens. language similar assembly.

almost working, i'm having trouble token. let me give example of token:

mov [eax], 4 mov [name],2 mov eax, [ebx] 

tokens: [eax], [ebx]

i can find want using pattern: \[(eax|ebx)\] error when use other patterns, believe because of '|'.

scanner = re.compile(r"""     ;(.)*                    # comment     |(\[-?[0-9]+\])          # memory_int     |(\[-?0x[0-9a-fa-f]+\])      # memory_hex     |(\[(eax|ebx)\])             # memory access registers     """, re.verbose)  match in re.finditer(scanner, lines[i]):             comment, memory_int, memory_hex, memory_reg = match.groups() 

error:

valueerror: many values unpack (expected 4) 

is there way replace '|' character?

the problem isn't because of | characters in:

    |(\[(eax|ebx)\])             # memory access registers 

it's because part of expression defining two capturing groups, 1 nested inside other — match.groups() returning more values unpacked, such first line:

(none, none, none, '[eax]', 'eax') 

one way avoid nested group instead use:

    |(\[eax\]|\[ebx\])          # memory access registers 

which result in being returned:

(none, none, none, '[eax]') 

as @shashank pointed out, use non-capturing group (?:...) syntax define nested possible register value patterns:

    |(\[(?:eax|ebx)\])          # memory access registers 

to achieve same thing. approach advantageous when there larger number of possible sub-patterns (and they're more complicated) because otherwise you'd need spell out entire pattern in full each possibility rather take advantage of commonality might have.