WordPress REST API how to assign different categories to a post using Python requests library

I've created a python script to create & post articles to WordPress site but it seems that the category in post data isn't getting assigned to the posts and it always gets assigned to uncategorized category, I am looking to only assign 1 category to the posts.

Am I doing something wrong here? WordPress REST API Docs aren't really helpful.

Here's the post creator function:

# Post creator function
def create_post(inputTitleSent, outputText):
    randomAuthor = random.choice(authorList)
    
    post_status = "draft"
    headers = {
        "Content-Type": "application/x-www-form-urlencoded"
    }
    post = {
        "title": inputTitleSent,
        "content": outputText,
        "status": post_status,
        "author": randomAuthor,
        "categories:": "6"
    }
    url = wp_base_url + "/wp-json/wp/v2/posts"
    response = requests.post(url, data=post, headers=headers, auth=(wp_username,wp_password))
    return response

I've tried "categories": 6 and I saw somewhere that it's suppose to be an array so I tried "categories": [6] and "categories": ['6'] but still posts get assigned to uncategorized category.

Just came across your question and couple of things caught my attention!

> "I saw somewhere that it's suppose to be an array so I tried "categories": [6] and "categories": ['6'] but still posts get assigned to uncategorized category."

General friendly tip on how to ask a better question here on SO:

• When you reach out for help, please provide people with the exact error(s)/warning(s) that you got on your app. This would be very helpful for people who are trying to help you debug your code! As a result, you would get your problem solved faster.

Back to your code, In addition to the typo that others already mentioned, I think the bug is in your headers. I've had success with the following steps in the past:

1- Authentication and Proper Permissions

Before we send anything, we would need to make sure that we could authenticate ourselves with wordpress. If so, then we would need to make sure that we have proper permission(s) to create a post. Since you didn't talk about authentication/permissions errors, then I'm going to assume that you are able to authenticate yourself and have proper permissions to create a post and we are safe to move on to the next step!

2- Using proper headers

Make sure to set the proper headers! Since we're going to feed wordpress a json object, then our headers should contain this:

headers = {"Content-Type": "application/json; charset=utf-8"}

3- Using json object as your post data/payload

I've had success with json objects in the past, so I would suggest that you use json object as your data/payload. And yes, categories should be an array of ids. In order to do so, you could do this:

post = {
  "title": inputTitleSent,
  "content": outputText,
  "status": post_status,
  "author": randomAuthor,
  "categories": [
    6,
    5
  ], 
}

4- Posting your data to the REST API

You could either use this:

response = requests.post(url, json=post, headers=headers, auth=(wp_username,wp_password))

Or this:

response = requests.post(url, data=post, headers=headers, auth=(wp_username,wp_password))

Theoretically, both ways, should work!

So, your entire code would be something like this:

# Post creator function
def create_post(inputTitleSent, outputText):

    post_status    = "draft"
    randomAuthor   = random.choice(authorList)

    headers = {
      "Content-Type": "application/json; charset=utf-8"
    }

    post = {
      "title": inputTitleSent,
      "content": outputText,
      "status": post_status,
      "author": randomAuthor,
      "categories": [
        6,
        5
      ],
    }

    url = wp_base_url + "/wp-json/wp/v2/posts"

    response = requests.post(url, json=post, headers=headers, auth=(wp_username,wp_password))

    # or 
    # response = requests.post(url, data=post, headers=headers, auth=(wp_username,wp_password))
    
    return response

Let me know if you could get it to work!

So, Basically, there is a typo in your POST payload "categories:": "6" you can simply remove the : from the double quote

def create_post(inputTitleSent, outputText):
    randomAuthor = random.choice(authorList)
    
    post_status = "draft"
    headers = {
        "Content-Type": "application/x-www-form-urlencoded"
    }
    post = {
        "title": inputTitleSent,
        "content": outputText,
        "status": post_status,
        "author": randomAuthor,
        "categories": [6]  # Replace "categories:" with "categories"
    }
    url = wp_base_url + "/wp-json/wp/v2/posts"
    response = requests.post(url, data=post, headers=headers, auth=(wp_username,wp_password))
    return response

You have an additional : character in the post payload under categories:

    post = {
        "title": inputTitleSent,
        "content": outputText,
        "status": post_status,
        "author": randomAuthor,
        "categories:": "6"
#                  ^
    }

Simply remove this and you'll get the results you're looking for:

# Post creator function
def create_post(inputTitleSent, outputText):
    randomAuthor = random.choice(authorList)
    
    post_status = "draft"
    headers = {
        "Content-Type": "application/x-www-form-urlencoded"
    }
    post = {
        "title": inputTitleSent,
        "content": outputText,
        "status": post_status,
        "author": randomAuthor,
        "categories": "6"
    }
    url = wp_base_url + "/wp-json/wp/v2/posts"
    response = requests.post(url, data=post, headers=headers, auth=(wp_username,wp_password))
    return response