Verwalten Sie Filter mit Pythons -m Option # 2

Im Artikel Letztes Mal habe ich mich auf die Verwaltung von Filtern in Python vorbereitet, also werde ich es dieses Mal tatsächlich schreiben. Es gibt jedoch viele Möglichkeiten, dies zu tun. Hier ist ein Beispiel mit "optparse". Dies ist ein Filter, der erstellt wurde, um eine große Anzahl von CSV-Dateien, die einmal erstellt wurden, in JSON zu konvertieren und zu verwenden. Einmal erstellt, kann er wiederverwendet werden, wenn Sie CSV später konvertieren möchten. Es ist praktisch, dass Sie sich keine Gedanken darüber machen müssen, wo sich die Dateien befinden. Da wir "optparse" verwenden, kann die Hilfe mit "-h" angezeigt werden.

$ python -m filter.csv2json -h
Usage: Command-line tool to convert CSV to JSON

  $ other cmd | python -m filter.csv2json [options]

Sample:
  $ cat sample.csv
  Year,Make,Model,Length
  1997,Ford,E350,2.34
  2000,Mercury,Cougar,2.38

  $ python -m filter.csv2json < sample.csv
  [
    {
      "Length": "2.34", 
      "Make": "Ford", 
      "Model": "E350", 
      "Year": "1997"
    },
    {
      "Length": "2.38", 
      "Make": "Mercury", 
      "Model": "Cougar", 
      "Year": "2000"
    }
  ]

  $ cat sample.csv | python -m filter.csv2json -t issf
  [
    {
      "Length": 2.34, 
      "Make": "Ford", 
      "Model": "E350", 
      "Year": 1997
    }, 
    {
      "Length": 2.38, 
      "Make": "Mercury", 
      "Model": "Cougar", 
      "Year": 2000
    }
  ]


Options:
  -h, --help            show this help message and exit
  -i INPUT, --input=INPUT
                        The path to the CSV file. It defaults to standard
                        input stream.
  -o OUTPUT, --output=OUTPUT
                        The path to the output JSON file. It defaults to
                        standard output stream.
  -d DELIMITER, --delimiter=DELIMITER
                        A one-character string used to separate fields. It
                        defaults to ','.
  -q QUOTECHAR, --quotechar=QUOTECHAR
                        A one-character string used to quote fields containing
                        special characters, such as the delimiter or
                        quotechar, or which contain new-line characters. It
                        defaults to '"'.
  -l LINETERMINATOR, --lineterminator=LINETERMINATOR
                        The string used to terminate lines. It defaults to
                        '\r\n'.
  -t TYPE DEFINITIONS, --typedef=TYPE DEFINITIONS
                        A string used to declare type of each field. i, f, s
                        are available. It defaults to treat all values as
                        string.

r"""Command-line tool to convert CSV to JSON.

  $ other cmd | python -m filter.csv2json [options]

Sample:
  $ cat sample.csv
  Year,Make,Model,Length
  1997,Ford,E350,2.34
  2000,Mercury,Cougar,2.38

  $ python -m filter.csv2json < sample.csv
  [
    {
      "Length": "2.34", 
      "Make": "Ford", 
      "Model": "E350", 
      "Year": "1997"
    },
    {
      "Length": "2.38", 
      "Make": "Mercury", 
      "Model": "Cougar", 
      "Year": "2000"
    }
  ]

  $ cat sample.csv | python -m filter.csv2json -t issf
  [
    {
      "Length": 2.34, 
      "Make": "Ford", 
      "Model": "E350", 
      "Year": 1997
    }, 
    {
      "Length": 2.38, 
      "Make": "Mercury", 
      "Model": "Cougar", 
      "Year": 2000
    }
  ]
"""

import sys
import csv
import json
import optparse


def main():
    parser = optparse.OptionParser(usage=__doc__)
    parser.add_option("-i", "--input", dest="input", metavar="INPUT",
                      default=sys.stdin,
                      help=("The path to the CSV file. It defaults to "
                            "standard input stream."))
    parser.add_option("-o", "--output", dest="output", metavar="OUTPUT",
                      default=sys.stdout,
                      help=("The path to the output JSON file. It defaults to "
                            "standard output stream."))
    parser.add_option("-d", "--delimiter", dest="delimiter",
                      metavar="DELIMITER", default=",",
                      help=("A one-character string used to separate fields. "
                            "It defaults to ','."))
    parser.add_option("-q", "--quotechar", dest="quotechar",
                      metavar="QUOTECHAR", default='"',
                      help=("A one-character string used to quote fields "
                            "containing special characters, such as the "
                            "delimiter or quotechar, or which contain "
                            "new-line characters. It defaults to '\"'."))
    parser.add_option("-l", "--lineterminator", dest="lineterminator",
                      metavar="LINETERMINATOR", default="\r\n",
                      help=("The string used to terminate lines. It defaults "
                            "to '\\r\\n'."))
    parser.add_option("-t", "--typedef", dest="typedef",
                      metavar="TYPE DEFINITIONS",
                      help=("A string used to declare type of each field. i, "
                            "f, s are available. It defaults to treat all "
                            "values as string."))

    opts, args = parser.parse_args()

    reader = csv.reader(opts.input,
                        delimiter=opts.delimiter,
                        quotechar=opts.quotechar,
                        lineterminator=opts.lineterminator)

    _iter = iter(reader)
    fields = next(_iter)
    
    if opts.typedef is None:
        typedef = 's' * len(fields)
    elif len(opts.typedef) < len(fields):
        typedef = opts.typedef + 's' * (len(fields) - len(opts.typedef))
    else:
        typedef = opts.typedef 

    cast = {
        's': lambda x: x,
        'i': lambda x: int(x),
        'f': lambda x: float(x),
    }

    obj = []
    for row in _iter:
        o = {}
        for i, [key, value] in enumerate(zip(fields, row)):
            o[key] = cast[typedef[i]](value)
        obj.append(o)

    json.dump(obj, opts.output, sort_keys=True, indent=2)
    opts.output.write('\n')


if __name__ == "__main__":
    main()