Format of complex number in Python
complex-numbers, python
Solution
It prints `0j` to indicate that it's still a `complex` value. You can also type it back in that way:
>>> 0j
0j
The rest is probably the result of the magic of IEEE 754 floating point representation, which makes a distinction between 0 and -0, the so-called signed zero. Basically, there's a single bit that says whether the number is positive or negative, regardless of whether the number happens to be zero. This explains why `1j * -1` gives something with a negative zero real part: the positive zero got multiplied by -1.
-0 is required by the standard to compare equal to +0, which explains why `(1j * -1).real == 0.0` still holds.
The reason that Python still decides to print the -0, is that in the complex world these make a difference for branch cuts, for instance in the `phase` function:
>>> phase(complex(-1.0, 0.0))
3.141592653589793
>>> phase(complex(-1.0, -0.0))
-3.141592653589793
This is about the imaginary part, not the real part, but it's easy to imagine situations where the sign of the real part would make a similar difference.
Problem
I am wondering about the way Python (3.3.0) prints complex numbers. I am looking for an explanation, not a way to change the print. Example: ``` >>> complex(1,1)-complex(1,1) 0j ``` Why doesn't it just print "0"? My guess is: to keep the output of type complex. Next example: ``` >>> complex(0,1)*-1 (-0-1j) ``` Well, a simple "-1j" or "(-1j)" would have done. And why "-0"?? Isn't that the same as +0? It doesn't seem to be a rounding problem: ``` >>> (complex(0,1)*-1).real == 0.0 True ``` And when the imaginary part gets positive, the -0 vanishes: ``` >>> complex(0,1) 1j >>> complex(0,1)*-1 (-0-1j) >>> complex(0,1)*-1*-1 1j ``` Yet another example: ``` >>> complex(0,1)*complex(0,1)*-1 (1-0j) >>> complex(0,1)*complex(0,1)*-1*-1 (-1+0j) >>> (complex(0,1)*complex(0,1)*-1).imag -0.0 ``` Am I missing something here?