I'm storing price as decimal(8,2) in mysql and I need to compare equality with a float in python.
Say I have 4.28 in database and select returns price = (Decimal(4.28),). I convert it to python decimal by decimal.Decimal(price[0]), but decimal.Decimal(price[0]) == 4.28 returns false.
Is there a way to compare equality directly other than comparing the difference with a small number, i.e.
decimal.Decimal(price[0]) - decimal.Decimal(4.28) < 0.01
Thanks
No, there are no other way to compare float representations of numbers for equality, but there are ways to make it practical:
decimal.Decimal(price[0]) - decimal.Decimal(4.28) < 0.01
should really be:
abs(decimal.Decimal(price[0]) - decimal.Decimal(4.28)) < 0.01
You can abstract the comparison:
def almost_equal(a, b, epsilon=1e-5):
"""returns true is the absolute value of the difference between a & b
is less than epsilon i/e a & b are almost equal, False otherwise
"""
return abs(a - b) < epsilon
abs() part. I'm only going to use it once, so probably no need to make a method for that.You need to convert what you're comparing to to a decimal:
decimal.Decimal('4.28') == decimal.Decimal(price[0])
price[0]is already decimal. Why are you trying to convert it to decimal again likedecimal.Decimal(price[0])? Becausedecimal.Decimal(decimal.Decimal(4.28))returnedDecimal('4.28000000000000024868995751603506505489349365234375')in my laptop.price[0]is a value return from database (using mysqldb) which is not Python decimal, it literallyDecimal(4.28)