perf(printing): make print_seq O(n) rather than quadratic

[oscarbenjamin]

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Release Notes

• printing
  • The pretty printer was made faster when printing large sequences (e.g. tuples, sets etc).

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• printing
  • The pretty printer was made faster when printing large sequences (e.g. tuples, sets etc). (#21169 by @oscarbenjamin)

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Update

The release notes on the wiki have been updated.

[oscarbenjamin]

With the PR:

In [3]: xs = symbols('x:1000')

In [4]: eqs = [x1 + sqrt(2)*x2 for x1, x2 in zip(xs[:-1], xs[1:])]

In [5]: eqs.append(xs[-1] - sqrt(3))

In [6]: s = linsolve(eqs, xs)

In [7]: %time ok = pretty(s)
CPU times: user 10.6 s, sys: 174 ms, total: 10.8 s
Wall time: 11 s

On master we have:

In [5]: %time ok = pretty(s)
CPU times: user 29.9 s, sys: 66.6 ms, total: 30 s
Wall time: 30 s

So that's quite a bit faster. It removes a quadratic algorithm and replaces it with one that is more linear. There might be other quadratic algorithms in there because it is still too slow.

[eric-wieser]

Looks reasonable, assuming stringPict.next is happy to take just one argument

[oscarbenjamin]

Thanks for the review!