2^n in binary is 10...0 (with n 0s), and 2^n - 1 is 11...1 (with n 1s). So if you do bitwise and (&) to 2^n and 2^n-1 you get all 0s. That's why you check if (num & (num - 1)) == 0.
Visar Zejnullahu On Sat, Sep 1, 2012 at 12:54 AM, Lazar <chaost...@gmail.com> wrote: > Hello, > > I'm fairly new to Python and still learning. > > Can someone please explain to me in what way the following function > checks if a number is a power of two? Basically, the second line of > code is what I can't really grasp: > > def is_power2(num): > return num != 0 and ((num & (num - 1)) == 0) > > Thank you, > Lazar > _______________________________________________ > Tutor maillist - Tutor@python.org > To unsubscribe or change subscription options: > http://mail.python.org/mailman/listinfo/tutor >
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