Running the PEG Parser benchmarks requires having memory_profiler installed.

In Tools/peg_generator:

➜  peg_generator git:(master) make time_stdlib
../../python -m zipfile -e data/xxl.zip data
../../python scripts/benchmark.py --parser=cpython --target=xxl compile
Traceback (most recent call last):
  File "/home/lysnikolaou/repos/cpython/Tools/peg_generator/scripts/benchmark.py", line 9, in <module>
    import memory_profiler
ModuleNotFoundError: No module named 'memory_profiler'

I propose to make that optional and only compute the timing benchmarks, in case memory_profiler is not available, since it's these benchmarks that are most important and most frequently run.

Why not just install it?

Because `make time` and all the related Makefile targets use the local built Python in the cpython parent directory. In order to install it, one would have to go through various steps, like installing openssl, configuring python with ssl support, building and installing python, creating a venv etc. Since it's more time-consuming that just running `make time` and since it's only needed for something that in most cases is not the most important thing, I think we can just go ahead and make it optional.

Is there a downside to this change I'm missing?

Soon nobody will remember to look at the memory stats at all. But I will review.

Doc/Makefile uses a virtual environment to install Sphinx and Sphinx extensions. I suggest to do something similar.

> Doc/Makefile uses a virtual environment to install Sphinx and Sphinx extensions. I suggest to do something similar.

I like this approach. Let me try it.

New changeset dc31800f86fbcd40ee616984820b885d8adaa6a7 by Lysandros Nikolaou in branch 'master':
bpo-40669: Install PEG benchmarking dependencies in a venv (GH-20183)
https://github.com/python/cpython/commit/dc31800f86fbcd40ee616984820b885d8adaa6a7

> bpo-40669: Install PEG benchmarking dependencies in a venv (GH-20183)

I like this approach :-)

New changeset 3764069f3ba2a7e932837ae19265059339dc86e3 by Pablo Galindo in branch 'master':
bpo-40669: Use requirements.pip when installing PEG dependencies (GH-20194)
https://github.com/python/cpython/commit/3764069f3ba2a7e932837ae19265059339dc86e3

New changeset 3d062829deadcb8355e97090aba47138eb9bc649 by Miss Islington (bot) in branch '3.9':
bpo-40669: Use requirements.pip when installing PEG dependencies (GH-20194)
https://github.com/python/cpython/commit/3d062829deadcb8355e97090aba47138eb9bc649