Default title "Post Object" after posting

I am new to django and I was creating a simple blog. I just added 'title', 'body', 'date' and 'time' fields. After hitting the save button, that particular post is 'added successfully' but the title of every post remains 'Post Object'. I tried 'manage.py makemigrations' and manage.py migrate commands after manage.py sync but it won't help either.

admin.py

from django.contrib import admin
from blog.models import Post
# Register your models here.

class PostAdmin(admin.ModelAdmin):
    search_fields = ["title"]

admin.site.register(Post, PostAdmin)

models.py

from django.db import models

# Create your models here.

    class Post(models.Model):
        title=models.CharField(max_length = 140)
        body=models.TextField()
        date=models.DateTimeField()

    def _unicode_(self):
        return self.title

settings.py """

INSTALLED_APPS = (
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'blog',
)

MIDDLEWARE_CLASSES = (
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.middleware.common.CommonMiddleware',
    'django.middleware.csrf.CsrfViewMiddleware',
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    'django.contrib.auth.middleware.SessionAuthenticationMiddleware',
    'django.contrib.messages.middleware.MessageMiddleware',
    'django.middleware.clickjacking.XFrameOptionsMiddleware',
    'django.middleware.security.SecurityMiddleware',
)

ROOT_URLCONF = 'mysite.urls'

TEMPLATES = [
    {
        'BACKEND': 'django.template.backends.django.DjangoTemplates',
        'DIRS': [],
        'APP_DIRS': True,
        'OPTIONS': {
            'context_processors': [
                'django.template.context_processors.debug',
                'django.template.context_processors.request',
                'django.contrib.auth.context_processors.auth',
                'django.contrib.messages.context_processors.messages',
            ],
        },
    },
]

WSGI_APPLICATION = 'mysite.wsgi.application'


# Database
# http://ift.tt/1EF8GkO

DATABASES = {
        'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': 'mysite.db'
    }
}


# Internationalization
# http://ift.tt/1CMZi8Y

LANGUAGE_CODE = 'en-us'

TIME_ZONE = 'UTC'

USE_I18N = True

USE_L10N = True

USE_TZ = True


# Static files (CSS, JavaScript, Images)
# http://ift.tt/1EF8GkR

STATIC_URL = '/static/'