def zero_or_positive_int(argument): 
    if argument is None: 
        return 0 
    elif argument == '0': 
        return 0 
    else: 
        return directives.positive_int(argument)
Converts a string into python positive integer including zero. 
dataset/ETHPy150Open rst2pdf/rst2pdf/rst2pdf/pygments_code_block_directive.py/zero_or_positive_int