计算后最有效的Python方法

Question

Ultimately, I am trying to accomplish the calculation of a number that gives me back 3 decimal places, and round it to 2 decimal places. What I have, is thus:

total = 175

tax = .0875

total += total * tax  # giving me my desired total
print total
>>> 190.3125

rounded = round(total, 2)  # giving me my desired decimal place
print rounded
>>> 190.31

I was thinking of doing the total and rounded line in one, but it looks jumbled...

Here is what I feel is the fastest way, but does not look as readable as I would like:

total = round((total + (total*tax)), 2)

print total
>>> 190.31

EDIT

Thank you guys for the input in the comments. It seems time is clearly not something to stress here & I am going to run with rounded = round(total, 2) for my code. Thanks again!

Answer 1

I think you should first think pythonically. What is the critical purpose of rounding a float? Do you need to use this rounded float to calculate later or you want to display it? Or you want to store it into a file or database with a consistent format? Different purposes lead to different methods.

If you want to use this rounded float to calculate later, you just don't need to round it. We should not do any additional process before the final calculation as it will only reduce the precision of results without any benefit.

If you want to display this rounded float, you can keep the precision inside variable and use string format: print "%.2f" % total . This will also print out what you want but won't make you lose precision.

If you want to store it into a file or a database, you can just go to rounded = round(total, 2) , it is really pythonic and useful.