Python float to int conversion
2.51 * 100 = 250.999999999997The int() function simply truncates the number at the decimal point, giving 250. Use
int(round(2.51*100)) to get 251 as an integer. In general, floating point numbers cannot be represented exactly. One should therefore be careful of round-off errors. As mentioned, this is not a Python-specific problem. It's a recurring problem in all computer languages.
What Every Computer Scientist Should Know About Floating-Point Arithmetic
Floating-point numbers cannot represent all the numbers. In particular, 2.51 cannot be represented by a floating-point number, and is represented by a number very close to it:
>>> print "%.16f" % 2.512.5099999999999998>>> 2.51*100250.99999999999997>>> 4.02*100401.99999999999994If you use int, which truncates the numbers, you get:
250401Have a look at the Decimal type.
Languages that use binary floating point representations (Python is one) cannot represent all fractional values exactly. If the result of your calculation is 250.99999999999 (and it might be), then taking the integer part will result in 250.
A canonical article on this topic is What Every Computer Scientist Should Know About Floating-Point Arithmetic.