On 07/19/2017 05:59 AM, Victor Stinner wrote:
Mercurial startup time is already 45.8x slower than Git whereas tested
Mercurial runs on Python 2.7.12. Now try to sell Python 3 to Mercurial
developers, with a startup time 2x - 3x slower...

When Matt Mackall spoke at the Python Language Summit some years back, I recall that he specifically complained about Python startup time.  He said Python 3 "didn't solve any problems for [them]"--they'd already solved their Unicode hygiene problems--and that Python's slow startup time was already a big problem for them.  Python 3 being even slower to start was absolutely one of the reasons why they didn't want to upgrade.

You might think "what's a few milliseconds matter".  But if you run hundreds of commands in a shell script it adds up.  git's speed is one of the few bright spots in its UX, and hg's comparative slowness here is a palpable disadvantage.

So please continue efforts for make Python startup even faster to beat
all other programming languages, and finally convince Mercurial to
upgrade ;-)

I believe Mercurial is, finally, slowly porting to Python 3.
Nevertheless, I can't really be annoyed or upset at them moving slowly to adopt Python 3, as Matt's objections were entirely legitimate.