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pythonrounding

Fix float precision with decimal numbers

a = 1

for x in range(5):
    a += 0.1
    print(a)

This is the result:

1.1
1.2000000000000002
1.3000000000000003
1.4000000000000004
1.5000000000000004

How can I fix this? Is the round() function the only way? Can I set the precision of a variable before setting its value?

Solution

  • can i set the precision of a variable before setting the value?

    Use the decimal module which, unlike float(), offers arbitrary precision and can represent decimal numbers exactly:

    >>> from decimal import Decimal, getcontext
>>> 
>>> getcontext().prec = 5
>>> 
>>> a = Decimal('1')
>>> 
>>> for x in range(5):
...     a += Decimal('0.1')  # note the use of `str` here
...     print(a)
... 
1.1000
1.2000
1.3000
1.4000
1.5000