Why/how do -1j and 0-1j become different strings?

Question

Why and how are -1j and 0 - 1j turned into different strings?

>>> a = -1j
>>> b = 0 - 1j
>>> a
(-0-1j)
>>> b
-1j

They're the same value of the same type:

>>> a == b
True
>>> type(a), type(b), type(a) is type(b)
(<class 'complex'>, <class 'complex'>, True)

But both str and repr turn them into different strings:

>>> str(a), str(b)
('(-0-1j)', '-1j')
>>> repr(a), repr(b)
('(-0-1j)', '-1j')

Why and how does that happen?

Note: This is in Python 3.6.4. In Python 2.7.14 they're both turned into '-1j'.

Maybe the -0 in `a`, although I doubt the downvoters were reading that carefully. — user2357112, Mar 08 '18 at 17:37
If the above question is _not_ a duplicate, it at least has some good discussion about the issue. I think [this](https://stackoverflow.com/a/13388276/3483203) answer might help. — user3483203, Mar 08 '18 at 17:45

score 4 · Accepted Answer · answered Mar 08 '18 at 17:39

a has a real component of -0.0, while b has a real component of 0.0. The 0.0 is omitted from the string representation.

-1j is treated as -(1j), where 1j has a real component of 0.0. That real component gets negated.

In 0 - 1j, the real components of both sides are 0, and the subtraction produces a real component of 0.

On Python 2, I think -1j probably hits the same special case used to make -2147483648 or -9223372036854775808 (platform-dependent) evaluate to an int instead of a long. The special-case handling seems to result in a real component of 0.0.

Ah, right, `-0.0` is a thing. That explains it. Still weird and inconvenient. Maybe I'll just add zero to get rid of it... both `-1j + 0` and `0 + -1j` get turned into the nicer `'-1j'`. — Stefan Pochmann, Mar 08 '18 at 17:45

Why/how do -1j and 0-1j become different strings?

1 Answers1