How to write a Celery task using postmarker

I am trying to write a celery task which uses the postmarker client library to send emails. This is a simple client library that calls the postmarkapp.com API endpoint.

# In tasks.py

@app.task(bind=True)
def send_email(...):
    """Sends a single email via Postmark."""
    postmark = PostmarkClient(...)
    response = postmark.emails.send(...)
    log.info('Postmark API send_email response %s', response)

But when I attempt to execute the task in my tests:

# in test_tasks.py

class PostmarkSendEmail(TestCase):
    def test_call_send_email(self):
        send_email(...)

I get the following error

TypeError: <@task: tasks.send_email of groot at 0x7f2c35b9e911> is not JSON serializable

My question is this, is it possible to use this client library within a celery task? is there something I can do to enable me to use this library in a celery task?

I found that the issue was with thebind=True parameter passed into the @app.task(). The solution was to remove that parameter:

@app.task()
def send_email(...):
    """Sends a single email via Postmark."""
    postmark = PostmarkClient(...)
    response = postmark.emails.send(...)
    log.info('Postmark API send_email response %s', response)

Alternatively, I could have added the self parameter to the send_email method:

@app.task(bind=True)
def send_email(self, ...):
    """Sends a single email via Postmark."""
    postmark = PostmarkClient(...)
    response = postmark.emails.send(...)
    log.info('Postmark API send_email response %s', response)

As the bind parameter, binds the method to the App instance.