Python: forcing precision on a floating point number in json?

Question

(update)

Here's the actual problem I'm seeing. Note that round() doesn't seem to be doing the trick.

Here's my code:

t0=time.time()
# stuff
t1=time.time()
perfdat={'et1' : round(t1-t0,6), 'et2': '%.6f'%(t1-t0)}

And the dict and json output, respectively:

{'et2': '0.010214', 'et1': 0.010214000000000001}

{"et2":"0.010214","et1":0.010214000000000001}

(end update)

I've got a floating point value that has a lot of extra digits of precision that I don't need. Is there a way to truncate those digits when formatting a json string?

I can get the truncation I need if I format the value as a string, but I would like to transmit the value as a (truncated) number.

import json
v=2.030000002

json.dumps({'x':v})     # would like to just have 2.030
'{"x": 2.030000002}'

s= '%.3f' % (v)         # like this, but not as a string
json.dumps({'x' : s})
'{"x": "2.030"}'

Answer 1

Wrap the number into a float:

>>> s = float('%.3f' % (v))
>>> json.dumps({'x' : s})
{"x": 2.03}