Android Code Snippet PyMod() - Python Modulo

In Python, the modulo (%) of a negative number is calculated differently providing us a more useful result for real-life applications.

For example, imagine a clock on the wall, it reads "July 4th 2017, 00:30".
- If you set it back one hour, it becomes "July 3rd 2017, 23:30".
- If you set it back 49 hours, it becomes "July 1st 2017, 23:30".

In Python:

print  -1 % 24 # = 23
print -49 % 24 # = 23

In B4X (also Java and C):

Log( -1 Mod 24) '= -1
Log(-49 Mod 24) '= -1

The trick:

Sub PyMod(x As Double, y As Double) As Double
    Return (y + (x Mod y)) Mod y
End Sub

Enjoy.

 

[Erel]

You can simplify it a bit:

Sub pyMod (x As Int, y As Int) As Int
   Return (y + x) Mod y
End Sub

I've also changed the types to Int so it will be supported by B4i.

 

[Ed Brown]

Return (y + x) Mod y

This will still result in -1 instead of 23 when x=-49 and y=24

 

[Erel]

You are correct...

I was mistaken as I sometimes use this code with degrees where the input is limited to -360 - 360 and therefore it is enough to add 360.

 

[Ed Brown]

I thought similarly as you.

This will return -23 where x < 0 and 23 where x > 0 (in cases where negative results are desirable)

(y*x - x) Mod y