Having problems with python rounding numbers when I call a specific entity from an array

Question

I have an array:

a = [0.313767818199811, 0.169656461527218, 0.934219696497667]

When I do

print a
[0.313767818199811, 0.169656461527218, 0.934219696497667]

print a[0]
0.3137678182

I need to preserve all the digits of each number in an array. I need a[0] to equal 0.313767818199811

Whats the best way to tell python to preserve the digits?

@jvallver: Try running this code: a = [0.313767818199811, 0.169656461527218, 0.934219696497667] print a print a[0] — user1808562, Nov 08 '12 at 08:29
`repr` returns the shortest string that rounds back to the original `float`, which could be from 1 to 17 digits, e.g. `0.10000000000000002` needs 17 digits. — Eryk Sun, Nov 08 '12 at 10:59

Marcelo Cantos · Answer 1 · 2012-11-08T08:32:09.340

4

a[0] does equal the full expansion. The print statement is truncating it (using str) for display purposes.

The following code might make this clearer. In particular, it explains the discrepancy between printing a and a[0] — str(a) calls repr (not str) on the elements of a:

>>> str(a)
'[0.313767818199811, 0.169656461527218, 0.934219696497667]'
>>> str(a[0])
'0.3137678182'

>>> repr(a)
'[0.313767818199811, 0.169656461527218, 0.934219696497667]'
>>> repr(a[0])
'0.313767818199811'

As suggested in the above code, you can display a[0] with the full precision as follows:

>>> print repr(a[0])
0.313767818199811

edited Nov 08 '12 at 08:32

answered Nov 08 '12 at 08:24

Marcelo Cantos

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Any idea on how to get the print statement to not do this? – user1808562 Nov 08 '12 at 08:27
@user1808562: I've just amended my answer with a way to display the full expansion. – Marcelo Cantos Nov 08 '12 at 08:29
@user1808562 just do `print repr(a[0])` – Ashwini Chaudhary Nov 08 '12 at 08:30
See http://stackoverflow.com/questions/1566936/easy-pretty-printing-of-floats-in-python – Lucas Hoepner Nov 08 '12 at 08:31

Nicolas · Accepted Answer · 2012-11-08T08:33:07.533

3

You can use:

print '%.15f' % a[0]
>> 0.313767818199811

It will display 15 digits after the decimal point.

edited Nov 08 '12 at 08:33

answered Nov 08 '12 at 08:26

Nicolas

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score 0 · Answer 3 · answered Nov 08 '12 at 08:25

0

you may need repr() here, print uses str() so your output is truncated:

In [13]: repr(a[0])
Out[13]: '0.313767818199811'

In [14]: repr(a[1])
Out[14]: '0.169656461527218'

answered Nov 08 '12 at 08:25

Ashwini Chaudhary

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Lucas Hoepner · Answer 4 · 2012-11-08T08:33:51.747

0

Use formatting: print '%.17f' % a[0] for 17 digits. If you ever have troubles with this again, google 'python float print precision'

edited Nov 08 '12 at 08:33

answered Nov 08 '12 at 08:26

Lucas Hoepner

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Having problems with python rounding numbers when I call a specific entity from an array

4 Answers4