Re: Custom sort order for YAML output

2009/9/22 Markus Jarderot <[email protected]>

>  [BEGIN]
>
> import yaml
>
> def represent_dict(self, data):
>     def key_function((key,value)):
>         # Prioritizes certain keys when sorting.
>         prio = {"model":0,"pk":1,"fields":2}.get(key,99)
>         return (prio, key)
>     items = data.items()
>     items.sort(key=key_function)
>     return self.represent_mapping(u'tag:yaml.org,2002:map', items)
>
> yaml.add_representer(represent_dict)
>
> [END]
>

Thank you for the suggestion. It doesn't quite work as it stands, but it got
me most of the way there and I figured out the last step with a little trial
and error. I'll explain. Suppose I do the following:

[BEGIN]
from optparse import OptionParser
import yaml

def represent_dict(self, data):
    def key_function((key,value)):
        # Prioritizes certain keys when sorting.
        prio = {"model":0,"pk":1,"fields":2}.get(key,99)
        return (prio, key)
    items = data.items()
    items.sort(key=key_function)
    return self.represent_mapping(u'tag:yaml.org,2002:map', items)

yaml.add_representer(represent_dict)

def main():
    # set up optparse
    usage = "usage: %prog [options] INPUT\nReads yaml from INPUT and returns
it as block style yaml to stdout"
    parser = OptionParser(usage)
    (options, args) = parser.parse_args()
    if len(args) != 1:
        parser.error("incorrect number of arguments")

    # get some flow style YAML from FILE1
    try:
        infile = open(args[0])
    except IOError:
        print 'Cannot open input file: ', args[0]
    else:
        input = infile.read()
        output = yaml.dump(yaml.load(input), default_flow_style=False)
        print output

# execute main()
if __name__ == "__main__":
    main()
[END]

Running: python yaml_to_block_style.py fixtures/dumped_data.yaml
yields:

Traceback (most recent call last):
  File "yaml_to_block_style.py", line 13, in <module>
    yaml.add_representer(represent_dict)
TypeError: add_representer() takes at least 2 arguments (1 given)


It seems that the first argument to add_representer should be a class name.
At first I thought that's not really appropriate in my case because I'm not
trying to represent a class (at least, not a class that's defined in my
code). Then I tried writing the add_representer line as:

yaml.add_representer(str, represent_dict)

since str is the class name of *input*, but this just yields:

Traceback (most recent call last):
  File "yaml_to_block_style.py", line 35, in <module>
    main()
  File "yaml_to_block_style.py", line 30, in main
    output = yaml.dump(yaml.load(input), default_flow_style=False)
  File "/home/me/django001/__init__.py", line 175, in dump

  File "/home/me/django001/__init__.py", line 165, in dump_all

  File "build/bdist.linux-i686/egg/yaml/representer.py", line 33, in
represent
  File "build/bdist.linux-i686/egg/yaml/representer.py", line 62, in
represent_data
  File "build/bdist.linux-i686/egg/yaml/representer.py", line 220, in
represent_list
  File "build/bdist.linux-i686/egg/yaml/representer.py", line 106, in
represent_sequence
  File "build/bdist.linux-i686/egg/yaml/representer.py", line 62, in
represent_data
  File "build/bdist.linux-i686/egg/yaml/representer.py", line 228, in
represent_dict
  File "build/bdist.linux-i686/egg/yaml/representer.py", line 127, in
represent_mapping
  File "build/bdist.linux-i686/egg/yaml/representer.py", line 62, in
represent_data
  File "yaml_to_block_style.py", line 9, in represent_dict
    items = data.items()
AttributeError: 'str' object has no attribute 'items'

shell returned 1


Finally, I tried changing the line to:

yaml.add_representer(dict, represent_dict)

And this worked!

Thank you,

Sam


> Sam Kuper skrev:
>
> Dear list,
>
> Bearing in mind I'm new to PyYAML, please could you help with the
> following.
>
> I'm using PyYAML to convert dumped YAML data from Django (which is flow
> style by default) into block style via the following Python script:
>
> [BEGIN]...[END]
>
> This works, but I'd like to output the data in the order shown here<http://docs.djangoproject.com/en/dev/howto/initial-data/#providing-initial-data-with-fixtures>- in other words, in the form:
>
> - model:
>   pk:
>   fields:
>
> I'd also like the fields to be sorted alphabetically.
>
> This ticket <http://pyyaml.org/ticket/23> suggests to me that this should
> be possible, but I'm not sure how best to insert a "custom representer"into the script above, in order to get the result I'm seeking.
>
> I'd be grateful for any help you can offer.
>
> Many thanks in advance,
>
> Sam
>
>

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