Adding and accessing headers to HTTP POST request in python [duplicate]

I'm django 1.11.7 with rest framework. I've been trying to access POST request headers but when I print it I get 'None'. I'm sending a request using the application postman. I've added a key-value pair in the Headers section and the request code looks like this:

POST /create_user HTTP/1.1
Host: localhost:8000
Content-Type: application/json
key1: value1
Cache-Control: no-cache
Postman-Token: # Postman token

{
  "username": "abcdefgh@123"
}

In my django app, my views.py file looks like this:

from django.shortcuts import render
from rest_framework.views import APIView
from rest_framework.response import Response
from rest_framework import status
import json

# Create your views here.
class CreateUser(APIView):
    def post(self, request, format='json'):
        try:
            request_data = json.loads(request.body.decode(encoding='UTF-8'))
            print 'Header data:', request.POST.get('key1')

The 'request' variable is of type Request (Django Rest Framework object). There is no exception raised. So how do I access the POST 'key1' header?