Raymond Hettinger <pyt...@rcn.com> writes: > On Aug 29, 8:33 am, Arnaud Delobelle <arno...@googlemail.com> wrote: >> ernest <nfdi...@gmail.com> writes: >> > Hi, >> >> > The operator module provides separate functions for >> > "in place" operations, such as iadd(), isub(), etc. >> > However, it appears that these functions don't really >> > do the operation in place: >> >> > In [34]: a = 4 >> >> > In [35]: operator.iadd(a, 3) >> > Out[35]: 7 >> >> > In [36]: a >> > Out[36]: 4 >> >> > So, what's the point? If you have to make the >> > assignment yourself... I don't understand. >> >> > Cheers, >> > Ernest >> >> That's because >> >> a += b >> >> is executed as: >> >> a = a.__iadd__(b) >> >> For immutable objects, (such as integers), a.__iadd__(b) returns a + b >> *and then* this value is assigned to a (or rather 'a' is bound to the >> value). So for immutables objects, iadd(a, b) is the same as a + b >> >> For mutable objects (such as lists), a.__iadd__(b) mutates the object >> *and then* returns self so that when the assignement is executed, 'a' >> will still be bound the the same object. E.g. if a = [1, 2] then >> >> a += [3] >> >> will first append 3 to the list and then reassign the list to 'a' (it is >> unnecessary in this case but if this step was omitted, the "in place" >> operators wouldn't work on immutables types). > > This is an excellent explanation. > Perhaps, you can submit a documentation > patch for the operator module so this > doesn't get lost. > > > Raymond
I have submitted a documentation patch: http://bugs.python.org/issue9717 -- Arnaud -- http://mail.python.org/mailman/listinfo/python-list
