requests.post(url, data={'interests':'football','interests':'basketball'})

I tried this, but it is not working. How would I post football and basketball in the interests field?

Dictionary keys must be unique, you can’t repeat them. You’d use a sequence of key-value tuples instead, and pass this to data:

requests.post(url, data=[('interests', 'football'), ('interests', 'basketball')])

Alternatively, make the values of the data dictionary lists; each value in the list is used as a separate parameter entry:

requests.post(url, data={'interests': ['football', 'basketball']})

Demo POST to http://httpbin.org:

>>> import requests
>>> url="http://httpbin.org/post"
>>> r = requests.post(url, data=[('interests', 'football'), ('interests', 'basketball')])
>>> r.request.body
'interests=football&interests=basketball'
>>> r.json()['form']
{u'interests': [u'football', u'basketball']}
>>> r = requests.post(url, data={'interests': ['football', 'basketball']})
>>> r.request.body
'interests=football&interests=basketball'
>>> r.json()['form']
{u'interests': [u'football', u'basketball']}

It is possible to use urllib3._collections.HTTPHeaderDict as a dictionary that has multiple values under a key:

from urllib3._collections import HTTPHeaderDict
data = HTTPHeaderDict()
data.add('interests', 'football')
data.add('interests', 'basketball')
requests.post(url, data=data)

Quoting from the docs directly:

The data argument can also have multiple values for each key. This can
be done by making data either a list of tuples or a dictionary with
lists as values. This is particularly useful when the form has
multiple elements that use the same key:

>>> payload_tuples = [('key1', 'value1'), ('key1', 'value2')]
>>> r1 = requests.post('https://httpbin.org/post', data=payload_tuples)
>>> payload_dict = {'key1': ['value1', 'value2']}
>>> r2 = requests.post('https://httpbin.org/post', data=payload_dict)
>>> print(r1.text)
{
  ...
  "form": {
    "key1": [
      "value1",
      "value2"
    ]
  },
  ...
}
>>> r1.text == r2.text
True