Python 单击参数定义定界符导致 CSV 错误 "delimiter" 必须是 1 个字符的字符串

Question

我正在尝试构建一个简单的 click 命令行应用程序，以使用一种类型的分隔符读入文件并使用不同的分隔符写出同一文件。我不想执行查找和替换之类的操作，因为列内可能有一些我不想触及的正确转义的定界符。

我编写了一个简单的基于点击的 CLI 来执行此操作，但是我在传递 \t 以创建制表符分隔文件时遇到了一些问题。

如以下错误所示，制表符分隔符未正确传递到 pandas 函数以写出新文件。当我在 CLI 中间打印定界符时，一切看起来都是正确的，所以我不确定这里发生了什么。

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()

这就是我将输入和输出定界符传递到 CLI 的方式：

python cli.py data.csv "," "\t"

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，您可以使用这样的回调：

代码：

import codecs

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

要使用回调，您可以执行以下操作：

@click.argument('escaped', callback=unescape)

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。

(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.

Python 单击参数定义定界符导致 CSV 错误 "delimiter" 必须是 1 个字符的字符串

Python click argument to define delimiter causes CSV error "delimiter" must be a 1-character string

python

pandas

python-click

代码：

这是如何工作的

测试代码：

结果：