Python单击参数定义分隔符导致CSV错误“分隔符”必须是1字符字符串

Question

我试图构建一个简单的click命令行应用程序，以读取具有一种分隔符类型的文件，并用不同的分隔符写出相同的文件。我不想做find和replace之类的操作，因为列中可能有一些我不想接触的转义分隔符。在

我编写了一个简单的基于click的CLI来实现这一点，但是在传递\t来创建一个制表符分隔的文件时遇到了一些问题。在

如下面的错误所示，制表符分隔符没有正确地传入pandas函数以写出新文件。当我在CLI中间打印出分隔符时，一切看起来都是正确的，所以我不确定这里发生了什么。在

import click
import pandas as pd

@click.command()
@click.argument('filename')
@click.argument('in_delimiter')
@click.argument('out_delimiter')
def cli(filename, in_delimiter, out_delimiter):

    """
    Command line interface to change file delimiters
    """

    # read in CSV file
    df = pd.read_csv(filename, sep=in_delimiter)
    print(len(df))

    # write out CSV file
    df.to_csv('output.csv', sep=out_delimiter, index=False)
    print("transformation complete")


if __name__ == '__main__':
    cli()

这是我将输入和输出分隔符传递到CLI的方式：

^{pr2}$

这是生成的错误：

Traceback (most recent call last):
  File "cli.py", line 24, in <module>
    cli()
  File "/home/curtis/Program_Files/miniconda3/envs/py36/lib/python3.6/site-packages/click/core.py", line 722, in __call__
    return self.main(*args, **kwargs)
  File "/home/curtis/Program_Files/miniconda3/envs/py36/lib/python3.6/site-packages/click/core.py", line 697, in main
    rv = self.invoke(ctx)
  File "/home/curtis/Program_Files/miniconda3/envs/py36/lib/python3.6/site-packages/click/core.py", line 895, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/home/curtis/Program_Files/miniconda3/envs/py36/lib/python3.6/site-packages/click/core.py", line 535, in invoke
    return callback(*args, **kwargs)
  File "cli.py", line 19, in cli
    df.to_csv('output.csv', sep=out_delimiter, index=False)
  File "/home/curtis/Program_Files/miniconda3/envs/py36/lib/python3.6/site-packages/pandas/core/frame.py", line 1745, in to_csv
    formatter.save()
  File "/home/curtis/Program_Files/miniconda3/envs/py36/lib/python3.6/site-packages/pandas/io/formats/csvs.py", line 169, in save
    self.writer = UnicodeWriter(f, **writer_kwargs)
  File "/home/curtis/Program_Files/miniconda3/envs/py36/lib/python3.6/site-packages/pandas/io/common.py", line 521, in UnicodeWriter
    return csv.writer(f, dialect=dialect, **kwds)
TypeError: "delimiter" must be a 1-character string

Answer 1

要处理转义字符，可以使用如下回调：

代码：

import codecs

def unescape(ctx, param, value):
    return codecs.getdecoder("unicode_escape")(value)[0]

要使用回调，可以执行以下操作：

^{pr2}$

这是如何工作的

这将使用unicode_escape编解码器处理传入的字符串。在

（Source）

测试代码：

import click

@click.command()
@click.argument('escaped', callback=unescape)
def cli(escaped):
    click.echo('len: {}, ord: {}'.format(len(escaped), ord(escaped)))


if __name__ == "__main__":
    commands = (
        r'\t',
        r'\n',
        '\t',
        ',',
        ' help',
    )

    import sys, time

    time.sleep(1)
    print('Click Version: {}'.format(click.__version__))
    print('Python Version: {}'.format(sys.version))
    for cmd in commands:
        try:
            time.sleep(0.1)
            print('     -')
            print('> ' + cmd)
            time.sleep(0.1)
            cli(cmd.split())

        except BaseException as exc:
            if str(exc) != '0' and \
                    not isinstance(exc, (click.ClickException, SystemExit)):
                raise

结果：

Click Version: 6.7
Python Version: 3.6.3 (v3.6.3:2c5fed8, Oct  3 2017, 18:11:49) [MSC v.1900 64 bit (AMD64)]
     -
> \t
len: 1, ord: 9
     -
> \n
len: 1, ord: 10
     -
>   
Usage: test.py [OPTIONS] ESCAPED

Error: Missing argument "escaped".
     -
> ,
len: 1, ord: 44
     -
>  help
Usage: test.py [OPTIONS] ESCAPED

Options:
   help  Show this message and exit.