确定一个数字中的千分之一

Question

If an aircraft is flying VFR in the US, if the heading is east, the altitude must be an odd thousand plus 500 feet (1500, 3500, 5500, etc). If flying west, the altitude must be an even thousand plus 500 feet (2500, 4500, 6500, etc). If I input a given altitude, but it is the wrong (odd or even) for the heading, how do I get Python to correct it next higher odd or even thousandths (1500 becomes 2500, 6500 becomes 7500, etc)? We never round down for altitudes. Thanks!

Answer 1

You could divide your altitude by 1000.0 and cast to an int which would drop the decimal:

if int(altitude/1000.0) % 2 == 0

Then you can do whatever you want with that information.

Answer 2

You can use math.ceil to do this:

>>> import math
>>> def next_alt(alt):
...    return (math.ceil(alt/1000)+1)*1000+500
... 
>>> next_alt(2500)
3500.0
>>> next_alt(3500)
4500.0

Which could then be used in a function this way:

def set_alt(heading, alt):
    if 0<=heading<=179:       # odd + 500
        return alt if alt / 1000 % 2 else (math.ceil(alt/1000)+1)*1000+500
    else:
        return alt if not alt / 1000 % 2 else (math.ceil(alt/1000)+1)*1000+500

(If Python 3, you need // instead of / )

>>> set_alt(290, 3500)
4500
>>> set_alt(90, 3500)
3500