Yes, agreed that startup time matters for scripting. I was talking to someone on the Google Cloud SDK (CLI) team recently, and they said startup time is a big deal for them ... it's especially problematic for shell tab completion helpers, because every time you press tab the shell has to load your Python program to do the completion. Even a couple dozen milliseconds is noticeable when you're typing quickly.


On Wed, Jul 19, 2017 at 3:15 PM, Larry Hastings <> wrote:

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.



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