I agree. It would be nice, but the impact on existing code is too large. I can easily imagine someone parsing the output of "print(somecomplexnumber)" and not considering spaces.

For the record, it would require changing complex.__repr__  (which is also complex.__str__) and complex.__format__.

Now that I look at the code, it seems that complex_format is only called from one place (complex_repr), with fixed parameters. It could be moved into complex_repr for what I think is a small improvement in readability.