Python script to decode serial data from Tenma 72-7735 Multimeter to give numbers displayed on lcd screen

lcd_decode.py

import serial
import time
import binascii
 
ser = serial.Serial(
    port='/dev/ttyUSB0',
    baudrate=2400,
    timeout = 0.1,
    stopbits=serial.STOPBITS_ONE,
    bytesize=serial.EIGHTBITS
)
 
ser.close()
ser.open()
 
ser.flush()
 
hex_vals = []
temp_str = ''
bin_vals = []
dmm_data = ''
lower_nibbles = []
for i in range (0, 14):       # make lists to store hex and binary values
    hex_vals.append('0')
    bin_vals.append(0)
    lower_nibbles.append(0)
     
     
def get_lower_nibbles(bin_vals):            # only keep the lower part of nibble
    for i in range(0, len(bin_vals)):
        temp_str = str(bin_vals[i])
        lower_nibbles[i] = str(temp_str[4:8])
     
    return(lower_nibbles)
 
a=[]
b=[]
c=[]
d=[]
digit = 0
 
for h in range(8):  # make a list for each digit to record which parts of seven segment are on or off
    a.append('0')
    b.append('0')
    c.append('0')
    d.append('0')
     
def lcd_get_num(lcd_array):                 ##  each digit corresponds to certain parts of seven segment display being on
    digit = 0
    if lcd_array == '1010000' : digit = 1
    if lcd_array =='1101101' : digit = 2
    if lcd_array == '1111001' : digit = 3
    if lcd_array == '0110011' : digit = 4
    if lcd_array == '1011011' : digit = 5
    if lcd_array == '1011111' : digit = 6
    if lcd_array == '1110000' : digit = 7
    if lcd_array == '1111111' : digit = 8
    if lcd_array == '1111011' : digit = 9
    if lcd_array == '1111110' : digit = 0
     
    return str(digit)
     
     
def decode_data(lower_nibbles):             #this function works out what numbers are being displated based on
    for i in range(1, len(lower_nibbles)):  # which parts of each seven segment digit are turned on
        temp_reg = lower_nibbles[i]
    #   print temp_reg
    #   print len(a)
        if (i==1):         ## first digit
            #print temp_reg[3]
            a[1] = temp_reg[3]
            a[6] = temp_reg[2]
            a[5] = temp_reg[1]
        if (i==2):
            a[2] = temp_reg[3]
            a[7] = temp_reg[2]
            a[3] = temp_reg[1]
            a[4] = temp_reg[0]
             
        if (i==3):
            b[1] = temp_reg[3]
            b[6] = temp_reg[2]
            b[5] = temp_reg[1]
             
        if (i==4):
            b[2] = temp_reg[3]
            b[7] = temp_reg[2]
            b[3] = temp_reg[1]
            b[4] = temp_reg[0]
             
        if (i==5):
            c[1] = temp_reg[3]
            c[6] = temp_reg[2]
            c[5] = temp_reg[1]
         
        if (i==6):
            c[2] = temp_reg[3]
            c[7] = temp_reg[2]
            c[3] = temp_reg[1]
            c[4] = temp_reg[0]
         
        if (i==7):
            d[1] = temp_reg[3]
            d[6] = temp_reg[2]
            d[5] = temp_reg[1]
         
        if (i==8):
            d[2] = temp_reg[3]
            d[7] = temp_reg[2]
            d[3] = temp_reg[1]
            d[4] = temp_reg[0]
    a.pop(0)
    b.pop(0)
    c.pop(0)
    d.pop(0)
    achar = ''.join(a)
    bchar = ''.join(b)
    cchar = ''.join(c)
    dchar = ''.join(d) 
    a.append('0')  
    b.append('0')
    c.append('0')              # this terrible piece of code would probably make                         
    d.append('0')             # Guido van Rossum cry 
     
    d1 = lcd_get_num(achar)
    d2 = lcd_get_num(bchar)
    d3 = lcd_get_num(cchar)
    d4 = lcd_get_num(dchar)
    print d1+d2+d3+d4              #print numbers displayed on LCD screen
     
    return(achar, bchar, cchar, dchar)
         
             
         
dmm_data = ""
 
while True:
    dmm_data = ""
    ser.flush()
    while dmm_data == "":                                #wait for a packet
        dmm_data = str(binascii.hexlify(ser.read(14)))
 
 
    g = 0                                               # concert hex values into binary
    for i in range(0, len(dmm_data), 2):
        bin_vals[g] = str( bin(int(dmm_data[i:i+2], 16))[2:].zfill(8))
        g=g+1
 
    #print bin_vals
 
    get_lower_nibbles(bin_vals)                       # only interested in lower nibble of each byte
    #print lower_nibbles
 
    decode_data(lower_nibbles)                        # from this data work out what numbers are displayed on screen
    time.sleep(0.5)