On Sat, Dec 01, 2012 at 09:19:57PM -0500, eryksun wrote: > On Sat, Dec 1, 2012 at 11:31 AM, Dave Angel <d...@davea.name> wrote: > > > > revdiag = [M[i][len(M)-1-i] for i in range(len(M)) ] > > You might sometimes see this using the bitwise invert operator ~ (i.e. > __invert__, operator.invert): > > >>> M = [[1, 2, 3], [4, 5, 6], [7, 8, 9]] > > >>> [M[i][~i] for i in xrange(len(M))] > [3, 5, 7]
Ew! There's something... smelly... about code using a bitwise-invert for indexing. Using it for bitwise operations is one thing. Using it to save writing two characters is just nasty. http://www.joelonsoftware.com/articles/Wrong.html http://c2.com/cgi/wiki?CodeSmell It smacks of low-level optimization tricks which make no sense in a high-level language like Python. You aren't writing optimized assembler, if you want -i-1 write -i-1 ! > ~i returns the value (-i - 1): Assuming certain implementation details about how integers are stored, namely that they are two-compliment rather than one-compliment or something more exotic. Okay, just about every computer made since 1960 uses two-compliment integers, but still, the effect of ~i depends on the way integers are represented internally rather than some property of integers as an abstract number. That makes it a code smell. And there is the risk that ~i will be misread as -i, which would be bad. -- Steven _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
