How do I grab the last portion of a log string and interpret it as json?

I am looking at a log message with the following format

datetime log_message_type message_type server {json_string}

So each line is separated by whitespace, always has the same fields for each line, and at the end has a json string with a variety of fields inside the json block.

I thought about doing this with a simple

with open('test.log', 'r') as f:
    for x in f:
        line = x.split()

        datetime         = line[0]
        log_message_type = line[1]
        message_type     = line[2]
        server           = line[3]
        json_string      = line[4]

This would have worked, except there are spaces in my json string, for example, something like this.

{ "foo" : "bar" }

So doing it in this way would split up my json string at the spaces. Is there any way I could use a regex or something to split on whitespace only until I get to the "json string" section of the line, and then preserve the rest of it? I tried doing something like

line = re.compile(".*\s.*\s.*\s.*\s").split(x)

To attempt to parse the line based on the 4 spaces before the json string portion, but I'm afraid I just don't know enough about how the regex system in python works. Could anyone give me a hand?

Edit : forgot to mention, I'm stuck with python 2.7 for this.