Python参数解析器，在h之前引发异常

Question

我不知道为什么会这样。我的理解是用户至少有机会在执行默认操作之前使用-h。

import os, sys, argparse
class argument_parser():
  # call on all our file type parsers in the sequence_anlysis_method

    def __init__(self):
        self.db_directory = os.path.dirname(os.path.abspath(sys.argv[0]))

        """A customized argument parser that does a LOT of error checking"""
        self.parser = argparse.ArgumentParser(
            prog="igblast")

        general = self.parser.add_argument_group(
            title="\nGeneral Settings")

        general.add_argument(
            "-x", '--executable',
            default="/usr/bin/igblastn",
            type=self._check_if_executable_exists,
            help="The location of the executable, default is /usr/bin/igblastn")

        self.args = self.parser.parse_args()

    def _check_if_executable_exists(self,x_path):
        if not os.path.exists(x_path):
            msg = "path to executable {0} does not exist, use -h for help\n".format(x_path)
            raise argparse.ArgumentTypeError(msg)
        if not os.access(x_path, os.R_OK):
            msg1 = "executable {0} does have not permission to run\n".format(x_path)
            raise argparse.ArgumentTypeError(msg1)
        else:
            return x_path

if __name__ == '__main__':
    argument_class = argument_parser()

现在，如果/usr/bin/igblastn在那里，那么就可以了，但是如果不是的话，只要调用这个程序就会在self\u check_中引发异常，如果有可执行文件。

^{pr2}$

根据我的理解，用户总是有机会运行--help或-h，或者在采取任何导致此参数错误的操作之前。我对arg解析器的理解不清楚吗？

Answer 1

您忘记在init__init__结束时运行^{}

class argument_parser(object):
    # call on all our file type parsers in the sequence_anlysis_method

    def __init__(self):
        self.db_directory = os.path.dirname(os.path.abspath(sys.argv[0]))

        """A customized argument parser that does a LOT of error checking"""
        self.parser = argparse.ArgumentParser(
            prog="igblast")

        general = self.parser.add_argument_group(
            title="\nGeneral Settings")

        general.add_argument(
            "-x", ' executable',
            default="/usr/bin/igblastn",
            type=self._check_if_executable_exists,
            help="The location of the executable, default is /usr/bin/igblastn")


        """ >>>>>>>>>>>>> add this line  <<<<<<<<<<< """
        self.parser.parse_args()

    def _check_if_executable_exists(self,x_path):
        if not os.path.exists(x_path):
            msg = "path to executable {0} does not exist, use -h for help\n".format(x_path)
            raise argparse.ArgumentTypeError(msg)
        if not os.access(x_path, os.R_OK):
            msg1 = "executable {0} does have not permission to run\n".format(x_path)
            raise argparse.ArgumentTypeError(msg1)
        else:
            return x_path

if __name__ == '__main__':
    argument_class = argument_parser()