On Fri, Sep 19, 2008 at 5:43 AM, Stephen McInerney <[EMAIL PROTECTED]> wrote: > Two questions about complex numbers: > > a) why are methods __add__,__mul__ defined but not the > operators '+','-','*','/' ?
This is true of all the numeric types. The method that implements + for a type is called __add__. Similarly * is implemented by __mul__. There are many more "special" methods that implement not only numeric operations but also things like indexing and iteration. A complete list of methods for numeric types is here: http://docs.python.org/ref/numeric-types.html > How can I bind the methods to the obvious operators (without creating a > custom > subclass of complex?) It seems pretty weird writing a.__add__(b) No need, this is done by the Python runtime. It converts a+b into a.__add__(b). (More or less...it could also end up as b.__radd__(a) or raise TypeError.) > b) Say I have a list ll which mixes real (float) and complex numbers. > ll = [1, 0.80-0.58j, 0.11+.2j] > What is the best Python idiom for getting the list of real parts of elements > of ll? > [lx.real for lx in ll] fails because only complex numbers have a 'real' > attribute, real numbers don't (slightly bizarre). > Unless I write the not-so-readable: > [(type(lx) is complex and lx.real or lx) for lx in ll] > or define my own function. You could also use getattr(lx, 'real', lx) if you prefer. > Do any of you see a need for a math.real() (or math.complex()) > function, which operates on all numeric types? > Then I could simply take the list comprehension > [real(lx) for lx in ll] > Is this worthy of a PEP? > It seems simple but overlooked. I guess someone agrees with you, at least in spirit...In Python 2.6 and 3.0, numeric types are in a hierarchy and integers and floats are also complex: In [13]: (5).real Out[13]: 5 In [18]: (5).imag Out[18]: 0 (The parentheses are needed to avoid a syntax error.) Also In [20]: import numbers In [21]: isinstance(5, numbers.Complex) Out[21]: True In [22]: isinstance(5.0, numbers.Complex) Out[22]: True _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
