[Python] How to catch exception output from Python subprocess.check_output()?

I'm trying to do a Bitcoin payment from within Python. In bash I would normally do this:

bitcoin sendtoaddress <bitcoin address> <amount>


So for example:

bitcoin sendtoaddress 1HoCUcbK9RbVnuaGQwiyaJGGAG6xrTPC9y 1.4214


If it is successful I get a transaction id as output, but if I try to transfer an amount larger than my bitcoin balance, I get the following output:

error: {"code":-4,"message":"Insufficient funds"}


In my Python program I now try to do the payment as follows:

import subprocess

try:
output = subprocess.check_output(['bitcoin', 'sendtoaddress', address, str(amount)])
except:
print "Unexpected error:", sys.exc_info()


If there's enough balance it works fine, but if there's not enough balance sys.exc_info() prints out this:

(<class 'subprocess.CalledProcessError'>, CalledProcessError(), <traceback object at 0x7f339599ac68>)


It doesn't include the error which I get on the command line though. So my question is; how can I get the outputted error ({"code":-4,"message":"Insufficient funds"}) from within Python?

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