Getting a different value when adding a float value in an integer (PYTHON)

Question

I am adding a float value in an integer using loops but the answer is different. Here is my code:

import time
test = 0
while True:
    test += 0.0001
    print(test)
    time.sleep(0.3)

When I ran it I should have got:

0.0001
0.0002
0.0003
0.0004
0.0005
.........

But I got:

0.0001
0.0002
0.00030000000000000003
0.0004
0.0005
0.0006000000000000001
0.0007000000000000001
0.0008000000000000001
0.0009000000000000002
0.0010000000000000002
0.0011000000000000003
0.0012000000000000003

Why it is so and how to solve this problem?

Possible duplicate of [How to avoid floating point errors?](https://stackoverflow.com/questions/19473770/how-to-avoid-floating-point-errors) — awesoon, Dec 02 '17 at 05:41
[What Every Computer Scientist Should Know About Floating-Point Arithmetic](https://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html) — kindall, Dec 02 '17 at 05:45

score 1 · Accepted Answer · answered Dec 02 '17 at 05:45

1

You can set the output precision using {:.4f} to keep four digits .

>>> pi
3.141592653589793
>>> print("{}".format(pi))
3.141592653589793
>>> print("{:.3f}".format(pi))
3.142
>>> print("{:.4f}".format(pi))
3.1416
>>> print("{:.5f}".format(pi))
3.14159

answered Dec 02 '17 at 05:45

Kinght 金

17,681
4
60
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Great . Is there any way to stop rounding off the number? – Nouman Dec 02 '17 at 05:47
You cann't represent the float number just as exact as you want, unless you set the precision. – Kinght 金 Dec 02 '17 at 05:48

score 0 · Answer 2 · answered Dec 02 '17 at 05:45

0

You solve the problem by seeking a deeper understanding of the inexact representation of rational, base 10 numbers by base 2 hardware.

See What Every Programmer Should Know About Floating-Point Arithmetic for a starter.

answered Dec 02 '17 at 05:45

Dave W. Smith

24,318
4
40
46

score 0 · Answer 3 · answered Dec 02 '17 at 05:45

0

It is inherent to the way binary floating-point are handled in operating systems. Have look here and here.

One of the possible solutions is to round the results to the decimal you want, here round to .4.

answered Dec 02 '17 at 05:45

Elliot

308
1
8

Getting a different value when adding a float value in an integer (PYTHON)

3 Answers3