在Python中指定csv.writer的格式 [英] Specifying formatting for csv.writer in Python

问题描述

我使用csv.DictWriter从一组字典输出csv文件。我使用以下函数：

I am using csv.DictWriter to output csv files from a set of dictionaries. I use the following function:

def dictlist2file(dictrows, filename, fieldnames, delimiter='\t',
          lineterminator='\n'):
    out_f = open(filename, 'w')

    # Write out header
    header = delimiter.join(fieldnames) + lineterminator
    out_f.write(header)

    # Write out dictionary
    data = csv.DictWriter(out_f, fieldnames,
              delimiter=delimiter,
              lineterminator=lineterminator)
    data.writerows(dictrows)
    out_f.close()

我的字典列表（dictrows）中的一些值是数字的，它们都是字典列表，例如浮动，我想指定这些的格式。例如，我可能想要使用％.2f序列化浮点数，而不是全精度。理想情况下，我想指定某种类型的映射，说明如何格式化每种类型，例如。

Some of the values in my dictionary list (dictrows) are numeric -- e.g. floats, and I'd like to specify the formatting of these. For example, I might want floats to be serialized with "%.2f" rather than full precision. Ideally, I'd like to specify some kind of mapping that says how to format each type, e.g.

{float: "%.2f"}

表示如果你看到一个浮动，用％.2f格式化。有没有一个简单的方法来做到这一点？我不想子类化DictWriter或任何复杂的东西 - 这似乎是非常通用的功能。

that says that if you see a float, format it with %.2f. Is there an easy way to do this? I don't want to subclass DictWriter or anything complicated like that -- this seems like very generic functionality.

如何这样做？

我可以想到的唯一的另一个解决方案是，而不是搞乱DictWriter的格式化，只是使用十进制包来指定浮点的十进制精度为％.2，这将导致序列化因此。不知道这是否是更好的解决方案？

The only other solution I can think of is: instead of messing with the formatting of DictWriter, just use the decimal package to specify the decimal precision of floats to be %.2 which will cause to be serialized as such. Don't know if this is a better solution?

非常感谢您的帮助。

推荐答案

class TypedWriter:
    """
    A CSV writer which will write rows to CSV file "f",
    which uses "fieldformats" to format fields.
    """

    def __init__(self, f, fieldnames, fieldformats, **kwds):
        self.writer = csv.DictWriter(f, fieldnames, **kwds)
        self.formats = fieldformats

    def writerow(self, row):
        self.writer.writerow(dict((k, self.formats[k] % v) 
                                  for k, v in row.iteritems()))

    def writerows(self, rows):
        for row in rows:
            self.writerow(row)

未测试。

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