Django ::: Slug in forms

plz help me. I get a trouble with slug in forms. I creat forms from models. This is models.py

class hire_article(models.Model):
hiring = models.CharField(max_length=50)
slug = models.SlugField(max_length=200)

This is forms

from django import forms
from django.forms import ModelForm, Textarea
from django.utils.translation import ugettext_lazy as _
import datetime
from .models import hire_article
from django.template.defaultfilters import slugify
from django.db import models
from django.contrib import admin

class postform(ModelForm):

    # class hire_articleAdmin(admin.ModelAdmin):
    #     prepopulated_fields = {"slug": ("hiring",)}
    class Meta:
        # more_infomation = MyFormField(max_length=200, required=False,
        #                    help_text="Use puns liberally")
        model = hire_article
        # exclude = ['slug']
        fields = '__all__'

This is admin.py

 from django.contrib import admin
    from .models import category, hire_article, localwork, salary,         mode_work, exp_year, degree, sex, language

class hire_articleAdmin(admin.ModelAdmin):
    prepopulated_fields = {"slug": ("hiring",)}
    list_display = ('id', 'hiring', 'publication_date', 'namecompany', )
    admin.site.register(hire_article, hire_articleAdmin)

It works only in admin . I want it work in forms too. Thank you in advance!