Defining precision of floating point number in Python

Question

I have some python code here

Code:

 t = 1
 xt = array([ -1.,-1. ])

 xt[0] = theta[0][0]* P_all_States[t-1][0] + theta[1][0]*P_all_States[t-1][1]

 xt[1] = theta[0][1]* P_all_States[t-1][0] + theta[1][1]*P_all_States[t-1][1]

 P_all_States[t][0] = xt[0]
 P_all_States[t][1] = xt[1]
 print ("Added probability distribution for time t = " + str(t) + " to P_all_States")
 print P_all_States

Output:

Added probability distribution for time t = 1 to P_all_States [[0.6, 0.4], [0.62000000000000011, 0.38000000000000006], [-1.0, -1.0], [-1.0, -1.0], [-1.0, -1.0], [-1.0, -1.0]]

How can I get the floating point numbers to round to 2 sigficant digits?

These are all floats, so Im not looking to convert these to strings, I want them to remain as floats

Thanks

related: Pretty-printing of numpy.array, namely np.set_printoptions(precision=2) — jfs
– jfs, Commented Oct 13, 2012 at 20:06

John Peters · Accepted Answer · 2012-10-13 20:09:14Z

3

I am not sure what you mean, but if you mean how you can modify their value to exactly 0.62, etc. : this is not possible with floats, because of their nature. You could use decimals instead of floats to get around this issue. If you mean how to print the floats with only 2 decimals, use:

print '{:3.2f}'.format(somefloat)

answered Oct 13, 2012 at 20:09

John Peters

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Zashas · Accepted Answer · 2012-10-13 20:05:12Z

2

>>> round(0.62000000000000011,2)
0.62

answered Oct 13, 2012 at 20:05

Zashas

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1 Comment

senderle Over a year ago

You should note that this doesn't actually result in the value 0.62. print decimal.Decimal(round(0.62000000000000011,2)) -> 0.61999999999999999555910790149937383830547332763671875.

Rudolf Mühlbauer · Accepted Answer · 2012-10-13 20:21:45Z

0

To convert the whole list, combine @Zashas answer with:

rounded = [ [round(a[0],2), round(a[1],2)] for a in P_all_States ]

edited Oct 13, 2012 at 20:21

answered Oct 13, 2012 at 20:10

Rudolf Mühlbauer

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2 Comments

John Peters Over a year ago

it is a list of list, so the above won' t do the job, need something like: rounded = [ [round(a[0],2), round(a[1],2)] for a in P_all_States ]

Rudolf Mühlbauer Over a year ago

sorry - did not realize that. well, you corrected it. thanks!

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