python argparse文件扩展名检查 [英] python argparse file extension checking

问题描述

argparse可以用于验证文件名cmd行参数的文件名扩展名吗?

can argparse be used to validate filename extensions for a filename cmd line parameter?

例如如果我有python脚本，则从cmd行运行:

e.g. if i have a python script i run from the cmd line:

$ script.py file.csv
$ script.py file.tab
$ script.py file.txt

我希望argparse接受第一个两个文件名cmd行选项，但拒绝第三个

i would like argparse to accept the 1st two filename cmd line options but reject the 3rd

我知道您可以执行以下操作:

i know you can do something like this:

parser = argparse.ArgumentParser()
parser.add_argument("fn", choices=["csv","tab"])
args = parser.parse_args()

为cmd行选项指定两个有效选择

to specify two valid choices for a cmd line option

我想要的是什么

parser.add_argument("fn", choices=["*.csv","*.tab"])

为cmd line选项指定两个有效的文件扩展名.不幸的是，这行不通-是否可以使用argparse来实现这一目标?

to specify two valid file extensions for the cmd line option. Unfortunately this doesn't work - is there a way to achieve this using argparse?

推荐答案

当然-您只需要指定一个适当的函数作为type.

Sure -- you just need to specify an appropriate function as the type.

import argparse
import os.path

parser = argparse.ArgumentParser()

def file_choices(choices,fname):
    ext = os.path.splitext(fname)[1][1:]
    if ext not in choices:
       parser.error("file doesn't end with one of {}".format(choices))
    return fname

parser.add_argument('fn',type=lambda s:file_choices(("csv","tab"),s))

parser.parse_args()

演示:

temp $ python test.py test.csv
temp $ python test.py test.foo
usage: test.py [-h] fn
test.py: error: file doesn't end with one of ('csv', 'tab')

---

这是一种可能更干净/更通用的方法:

---

Here's a possibly more clean/general way to do it:

import argparse
import os.path

def CheckExt(choices):
    class Act(argparse.Action):
        def __call__(self,parser,namespace,fname,option_string=None):
            ext = os.path.splitext(fname)[1][1:]
            if ext not in choices:
                option_string = '({})'.format(option_string) if option_string else ''
                parser.error("file doesn't end with one of {}{}".format(choices,option_string))
            else:
                setattr(namespace,self.dest,fname)

    return Act

parser = argparse.ArgumentParser()
parser.add_argument('fn',action=CheckExt({'csv','txt'}))

print parser.parse_args()

这里的缺点是代码在某些方面变得更加复杂-结果是，当您实际格式化参数时，接口变得更整洁了.

The downside here is that the code is getting a bit more complicated in some ways -- The upshot is that the interface gets a good bit cleaner when you actually go to format your arguments.

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