On Saturday, 2 October 2021 at 13:48:39 UTC+1, hongy...@gmail.com wrote: > On Saturday, October 2, 2021 at 4:59:54 PM UTC+8, ju...@diegidio.name wrote: > > On Saturday, 2 October 2021 at 10:34:27 UTC+2, hongy...@gmail.com wrote: > > > See the following testings: > > > > > > In [24]: a=3.1415926535897932384626433832795028841971 > > > In [27]: -a > > > Out[27]: -3.141592653589793 > > You've never heard of floating-point? Double precision has 53 significant > > bits of mantissa, corresponding approximately to 16 decimal digits. > > <https://en.wikipedia.org/wiki/Double-precision_floating-point_format#IEEE_754_double-precision_binary_floating-point_format:_binary64> > > > > > In [17]: ~-+1 > > > Out[17]: 0 > > << The unary ~ (invert) operator yields the bitwise inversion of its > > integer argument. The bitwise inversion of x is defined as -(x+1). It only > > applies to integral numbers or to custom objects that override the > > __invert__() special method. >> > > <https://docs.python.org/3/reference/expressions.html#unary-arithmetic-and-bitwise-operations> > > > > > I'm very puzzled by these operators. Any hints will be highly > > > appreciated. > > Try and read the proverbial manual: that's truly a fundamental skill... > Thank you for your explanation. Then what about the following questions?: > > 1. Should `+' and `-' be classified as binary operators or unary operators?
Both. See sections 6.6 and 6.7 of the documentation at https://docs.python.org/3/reference/expressions.html > As we all know, `a + b', and `a - b' are the normal ways we do basic > arithmetic operations. Really? Don't you ever write something like "x = -y"? Or do you habitually write "x = 0 - y" or "x = 0.0 - y"? > 2. See the following testings: > > In [20]: bool(int(True)) int(True) -> 1 bool(1) -> True > Out[20]: True > > In [21]: bool(~int(True)) int(True) -> 1 ~1 -> -2 bool(-2) -> True > Out[21]: True > > In [22]: bool(~~int(True)) int(True) -> 1 ~1 -> -2 # these two operations ~(-2) -> 1 # cancel each other out bool(1) -> True > Out[22]: True > > In [23]: bool(~~~int(True)) Because two consecutive bit-inversions cancel each other out; this is just a complicated re-statement of operation [21], above > Out[23]: True > > In [24]: bool(int(False)) int(False) -> 0 bool(0) -> False > Out[24]: False > > In [25]: bool(~int(False)) int(False) -> 0 ~0 -> -1 bool(-1) -> True > Out[25]: True > > In [26]: bool(~~int(False)) Again, two consecutive inversions cancel each other out so this is just an over-complicated re-statement of [24] > Out[26]: False > > In [27]: bool(~~~int(False)) Likewise, this is the equivalent of re-stating [25] > Out[27]: True > > Why can’t/shouldn't we get something similar results for both `True' and > `False' in the above testings? Sorry, I can't parse that. -- https://mail.python.org/mailman/listinfo/python-list
