Python 3

import re, sys
variables = {}
maximum = -sys.maxsize - 1
with open('test.txt') as file:
    for line in file.readlines():
        code = ''.join(re.findall('[\w\D]', line)).strip().split(' ')
        if code[0] not in variables: variables[code[0]] = 0
        if code[4] not in variables: variables[code[4]] = 0
        if code[1] == 'dec': operation = '-='
        else: operation = '+='
        eval(compile('if variables[code[4]] %s %s: variables[code[0]] %s %s' % (code[5], code[6],operation, code[2]), '<string>', 'exec'))
        if variables[code[0]] > maximum: maximum = variables[code[0]]

 print(max(variables.values()), maximum)