how to use switch case in python , where you call a specific function in each case?

i wrote this code where i have to read instructions from a file and have to recognise every instruction, and at the end i want to put the instructions in a list.

i created a list of objects to describe each instruction (the opcode,the source ..)

my problem is that when i read each line(instruction) from the file, i wanna get the opcode of the instruction to know how to work and extract the other information from the instruction line i tried to do switch case like this :

def OpcodeSwitcher(inst_opcode) :
    switcher = {
         'ADD': add_sub_branch(line), #function I call when the instruction is ADD
         'SUB': print(1)
 }

and then called this function which the opcode I extracted from my line but I got struck in infinity loop !

i just can't figure it out , any help ?

here is an example of a very small file :

ADD $3, $0, 4
SUB $7, $0, 1
# Program ends with infinite loop (avoid fall-through to undefined data following the end of the program)
# Data for this program. Any other location that is not explicitly set is implicitly set to zero.
D@0x000032A0
0x12345678
0xFFFFFFFF

here is the main file:

    import sys
    import memory as Memory


    # main

    file_name = sys.argv[1]
    print("Loading memory image file:", file_name)
    Memory.sim_mem_reset(file_name)

and here is the memory file :

    import sys


    instructionsList = []


    class Sim_cmd(object) :
        def __init__(self, opcode, src1, src2,isSrc2Imm,dst) :
            self.opcode=opcode
            self.src1=src1
            self.src2=src2
            self.isSrc2Imm=isSrc2Imm
            self.dst=dst




    def get_inst(line,inst_num) :
        inst_opcode=line.split(' ', 1)[0]

        # here I am trying to do a case switch statement on the inst_opcode
        # for example if the opcode is "ADD" I would like to call a function to handle 
        # this line to fill the instructionsList which means to do something like this
        # instructionsList.append(Sim_cmd(inst_opcode,0,0,0,0))



    def sim_mem_reset(memFileName):
        with open(memFileName, 'r+') as fileName:
            for line in fileName:
                if line[0] == '#' or len(line.strip()) == 0:
                    continue

                inst = 0
                while len(line.strip()) != 0 and line[0] != '#' and line[0] != 'D':
                    get_inst(line, inst)
                    inst += 1

                # here the data memory begin
                if line[0] == 'D' and line[1] == '@':
                #some code