Requests: The Difference Between Params and Data

This question pops up a lot on Stack Overflow, on GitHub, and in the IRC channel, so I thought I’d write a short post to address it. The question is, broadly, this:

How do I send data on a POST? I tried params, but that didn’t work!

The answer is that Requests has two different arguments for ‘sending’ data on a HTTP request: params and data. Each one does something different, but in their simplest form they both accept a dictionary of keys and values.

params is all about the query string, and so is primarily used on GET requests. To see it in action, take a look at this chunk of code:

>>> params = {'hi': 'there', 'what': 'ho'}
>>> r = requests.get('http://httpbin.org/get', params=params)
>>> print r.request.url
http://httpbin.org/get?hi=there&what=ho

The key take away here is that the data that was passed to params ended up in the URL query string. This is what it’s for. Any string data passed in there will be correctly escaped and encoded, then added to the URL.

data works differently: it’s all about the request body. Again:

>>> data = {'hi': 'there', 'what': 'ho'}
>>> r = requests.post('http://httpbin.org/post', data=data)
>>> print r.request.body
what=ho&hi=there

Why are two different parameters used? Why don’t we just have params set the request body on a POST, and the query string on anything else? The answer is that you might want to use a query string and a request body at the same time. There needs to be a different keyword.

So now you know: params for query string, data for request body. Simple.