ModelForm基类：添加bootstrap新式

from django import forms

class BootStrapModelForm(forms.ModelForm):
	def __init__(self, *args, **kwargs):
		super().__init__(*args, **kwargs)
		# 循环ModelForm中的所有字段，给每个字段的插件设置
		for name, field in self.fields.items():
			# 字段中有属性，保留原来的属性，没有属性，才增加。
			if field.widget.attrs:
				field.widget.attrs['class'] = 'form-control'
				field.widget.attrs['placeholder'] = field.label
			else:
				field.widget.attrs = {
					'class': 'form-control',
					'placeholder': field.label
				}