Django，模型字段定义的额外参数

问题描述

我想在model.Field基类中添加额外的参数以后使用而无需在Form或ModelForm类中再次定义字段的额外选项.

I wanted to add extra argument to model.Field base class touse later without defining field's extra options again in Form or ModelForm class.

然后我可以添加额外的参数:

And I can add extra argument with:

class Poll(models.Model):

    question = models.CharField(max_length=200,
                                extra= { 'widget': 'xw', 
                                         'admin_list_order': 3 })

    pub_date = models.DateTimeField('date published')

我可以通过以下方式访问额外的arg:

I can access extra arg with:

(InteractiveConsole)
>>> from polls.models import Poll
>>> Poll._meta.fields[1].extra
{'widget': 'xw', 'admin_list_order': 3}
>>> 

这是添加额外参数的Python适当方法吗?

Is this an appropriate, Pythonic way to add an extra argument?

from django.db import models

# save old __init__ function of Field class
__oInit = models.Field.__init__

# define a new one to accept 'extra' arg
def __xinit__(self, *args, **kwargs):

    #chek if extra arg exist
    if kwargs.has_key('extra'):
        self.extra = kwargs.pop('extra')

    #call real __init__ 
    __oInit(self, *args, **kwargs)

# replace init with new one
models.Field.__init__ = __xinit__

推荐答案

如果他们向字段添加extra自变量，则可能会中断.而且一般不建议使用 monkeypatches .您可以通过向Field基类中添加方法来走一条更安全的路线:

This could break if they ever add an extra argument to a field. And monkeypatches are discouraged in general. You could go a safer route by adding a method to the Field base class:

def set_extra(self, **kwargs):
    self.extra = kwargs
    return self
models.Field.set_extra = set_extra

然后像这样定义模型:

class Poll(models.Model):
    question = models.CharField(max_length=200).set_extra(
            widget='xw', admin_list_order=3)

---

has_key被认为是 unpythonic ，检查密钥是否存在的首选方法是:

---

has_key is considered unpythonic, preferred way to check for key presence is:

if 'extra' in kwargs:
    self.extra = kwargs.pop('extra')

更多的 pythonic 会尝试并捕获失败:

More pythonic would be just trying it and catching failure:

try:
    self.extra = kwargs.pop('extra')
except KeyError:
    pass

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