Generic CSV export admin action factory with relationship spanning fields and labels

import csv
from django.http import HttpResponse
 
 
def prep_field(obj, field):
    """ Returns the field as a unicode string. If the field is a callable, it
    attempts to call it first, without arguments.
    """
    if '__' in field:
        bits = field.split('__')
        field = bits.pop()
 
        for bit in bits:
            obj = getattr(obj, bit, None)
 
            if obj is None:
                return ""
 
    attr = getattr(obj, field)
    output = attr() if callable(attr) else attr
    return unicode(output).encode('utf-8') if output else ""
 
 
def export_csv_action(description="Export as CSV", fields=None, exclude=None, header=True):
    """ This function returns an export csv action. """
    def export_as_csv(modeladmin, request, queryset):
        """ Generic csv export admin action.
        Based on http://djangosnippets.org/snippets/2712/
        """
        opts = modeladmin.model._meta
        field_names = [field.name for field in opts.fields]
        labels = []
 
        if exclude:
            field_names = [f for f in field_names if f not in exclude]
 
        elif fields:
            field_names = [field for field, _ in fields]
            labels = [label for _, label in fields]
 
        response = HttpResponse(mimetype='text/csv')
        response['Content-Disposition'] = 'attachment; filename=%s.csv' % (
                unicode(opts).replace('.', '_')
            )
 
        writer = csv.writer(response)
 
        if header:
            writer.writerow(labels if labels else field_names)
 
        for obj in queryset:
            writer.writerow([prep_field(obj, field) for field in field_names])
        return response
    export_as_csv.short_description = description
    return export_as_csv


## Example Usage

from django.contrib import admin

 
class ExampleModelAdmin(admin.ModelAdmin):
    raw_id_fields = ('field1',)
    list_display = ('field1', 'field2', 'field3',)
    actions = [
        export_csv_action("Export Sepecial Report",
            fields=[
                ('field1', 'label1'),
                ('foreign_key1__foreign_key2__name', 'label2'),
                ('field3', 'label3'),
            ],
            header=True
        ),
    ]
 
admin.site.register(ExampleMode, ExampleModelAdmin)