Question

如何通过字典理解迭代字典来处理它。

>>> mime_types={
    '.xbm': 'image/x-xbitmap',
    '.dwg': 'image/vnd.dwg',
    '.fst': 'image/vnd.fst',
    '.tif': 'image/tiff',
    '.gif': 'image/gif',
    '.ras': 'image/x-cmu-raster',
    '.pic': 'image/x-pict',
    '.fh':  'image/x-freehand',
    '.djvu':'image/vnd.djvu',
    '.ppm': 'image/x-portable-pixmap',
    '.fh4': 'image/x-freehand',
    '.cgm': 'image/cgm',
    '.xwd': 'image/x-xwindowdump',
    '.g3':  'image/g3fax',
    '.png': 'image/png',
    '.npx': 'image/vnd.net-fpx',
    '.rlc': 'image/vnd.fujixerox.edmics-rlc',
    '.svgz':'image/svg+xml',
    '.mmr': 'image/vnd.fujixerox.edmics-mmr',
    '.psd': 'image/vnd.adobe.photoshop',
    '.oti': 'application/vnd.oasis.opendocument.image-template',
    '.tiff':'image/tiff',
    '.wbmp':'image/vnd.wap.wbmp'
}

>>> {(key,val) for key, val in mime_types.items() if "image/tiff" == val}

这是返回的结果：

set([('.tiff', 'image/tiff'), ('.tif', 'image/tiff')])

但我期待

('.tif', 'image/tiff')

如何修改该结果以获取如下字典：

{'.tif': 'image/tiff'}

Answer 1

替换

{(key,val) for key, val in mime_types.items() if "image/tiff" == val}

带

{key: val for key, val in mime_types.items() if "image/tiff" == val}

Answer 2

你可以像@Anubhav Chattoraj建议的那样dictionary comprehension。

或者将generator expr作为参数传递给函数dict：

In [165]: dict((k, mimes[k]) for k in mimes if mimes[k] == "image/tiff")
Out[165]: {'.tif': 'image/tiff', '.tiff': 'image/tiff'}

不要混合两种方式..

Answer 3

表达式：

{ value for bar in iterable }

是set comprehension。

为了执行 dict理解，您必须为Python提供一组由:分隔的键值对：

{ key: value for bar in iterable }

Answer 4

you can try something like this

>>> print {k : v for k, v in mime_types.iteritems()}

Another Simple Example

    >>> print {i : chr(65+i) for i in range(4)}
    {0 : 'A', 1 : 'B', 2 : 'C', 3 : 'D'}

通过理解迭代字典并获得字典

4 个答案: