Python argparse在参数前添加了额外的空间 [英] Python argparse adds extra space before an argument

问题描述

我发现argparse在参数前增加了一个额外的空间.根据下面的示例代码

I found that argparse adds an extra space before an argument. Based on the example code below

def parse_arguments():
    parser = argparse.ArgumentParser(
    prog='sample',
    description='bla bla',
    parser.add_argument('-s', '--search', dest='pattern', required=True,
    help='search path pattern (e.g. /dir1/dir2/*.ext)')

    args = parser.parse_args()

    if args.pattern[0] == ' ':
        print "One space is added to the argument"
    return args

并在交互式shell中测试为:

and testing in interactive shell as:

import sys
sys.argv = ['', '-s /Users/user/Desktop/test']
execfile('test.py')

将参数提供为sys.argv = ['', '-s=/Users/user/Desktop/test']不会引起这种加法(来自 https://stackoverflow.com/a/36376287/2101864 ).

Providing the argument as sys.argv = ['', '-s=/Users/user/Desktop/test'] does not cause such an addition (inspiring from https://stackoverflow.com/a/36376287/2101864).

这是记录在案的行为还是我错过了某些事情?因为通常有一个普通用户提供参数，所以在参数标签和值之间添加了一个空格.

Is it a documented behavior or do I miss something? Because it is typical that a regular user provide argument adding a space between argument tag and value.

推荐答案

如果直接执行test.py，将不会出现多余的空间.在交互式外壳程序中会发生这种情况，这是因为您在执行test.py之前将sys.argv设置为.

If you directly execute test.py, the extra space won't occur. That happens in the interactive shell because of what you're setting sys.argv to before executing test.py.

sys.argv = ['', '-s /Users/user/Desktop/test']

但是从终端运行脚本并检查sys.argv时，您得到:

But when running the script from the terminal and checking sys.argv, you get:

['test.py', '-s', '/Users/user/Desktop/test']

从终端运行时，它还会忽略-s和该值之间的多个空格.

It also ignores multiple spaces between -s and the value when running from terminal.

shell/终端已经为脚本单独提供了每个参数(Python将它们放入列表中).因此，第二个参数仅是-s而不是-s /Users/user/Desktop/test. 在交互式外壳中执行sys.argv = ['', '-s', '/Users/user/Desktop/test']会给出正确的结果.

The shell/terminal already provides each parameter separately to the script (and Python puts them into a list). So the 2nd param is only -s and not -s /Users/user/Desktop/test. Doing sys.argv = ['', '-s', '/Users/user/Desktop/test'] in the interactive shell gives the right result.

argparse 可能所做的工作是扫描sys.argv中的每个arg，并查找所有参数名称模式-s或--search.一旦找到，此后的所有内容即为参数值. -s=/Users/user/Desktop/test中的=是标准的arg=value表示法(在过去更是如此)，因此将其解释为参数与其值之间的分隔符.

What argparse probably does is scan each arg in sys.argv and look for all argument name patterns, -s or --search. Once found, everything after that is the argument value. The = in -s=/Users/user/Desktop/test is standard arg=value notation (more so in the past), so it interprets that as the delimiter between an argument and its value.

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