math.nroot [was Re: A brief question.]
tim.peters at gmail.com
Sun Jul 3 23:04:20 CEST 2005
> So, is there a way of generating and testing for infinities and NaNs
> that's portable across platforms and versions of python?
Not that I know of, and certainly no simple way.
> If not, could we perhaps have some constants in the math module for them?
See PEP 754 for this.
>> Read the manual for the precedence rules. -x**y groups as -(x**y). -1.0
>> is the correct answer. If you intended (-x)**y, then you need to insert
>> parentheses to force that order.
> So i see. Any idea why that precedence order was chosen? It goes against
> conventional mathematical notation, as well as established practice in
> other languages.
Eh? For example, Fortran and Macsyma also give exponentiation higher
precedence than unary minus. From my POV, Python's choice here was
> Also, would it be a good idea for (-1.0) ** 0.5 to evaluate to 1.0j? It
> seems a shame to have complex numbers in the language and then miss this
> opportunity to use them!
It's generally true in Python that complex numbers are output only if
complex numbers are input or you explicitly use a function from the
cmath module. For example,
>>> import math, cmath
Traceback (most recent call last):
File "<stdin>", line 1, in ?
ValueError: math domain error
The presumption is that a complex result is more likely the result of
program error than intent for most applications. The relative handful
of programmers who expect complex results can get them easily, though.
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