How to convert a negative number to positive?

Question

>>> n = -42
>>> -n       # if you know n is negative
42
>>> abs(n)   # for any n
42

Don't forget to check the docs.

simply multiplying by -1 works in both ways ...

>>> -10 * -1
10
>>> 10 * -1
-10

If "keep a positive one" means you want a positive number to stay positive, but also convert a negative number to positive, use abs():

>>> abs(-1)
1
>>> abs(1)
1

The inbuilt function abs() would do the trick.

positivenum = abs(negativenum)

In [6]: x = -2
In [7]: x
Out[7]: -2

In [8]: abs(x)
Out[8]: 2

Actually abs will return the absolute value of any number. Absolute value is always a non-negative number.