Have a fix for this that I'll send off shortly.

What I see with the current head (my username was replaced with "Foo Bar" in this example:
> Using "C:\Users\Foo Bar\cpython\PCbuild\\..\externals\pythonx86\tools\python.exe" (found in externals directory)
> Bar\cpython\PCbuild\\..\externals\pythonx86\tools\python.exe""=="" was unexpected at this time.

My theory, window's turning:
> C:\Users\Foo Bar
into
> "C:\Users\Foo Bar"
and this is colliding with our use of "%PYTHON%", creating double quotes, or:
> ""C:\Users\Foo Bar""
which, of course:
> if ""C:\Users\Foo Bar""==""
does not make sense as a statement.

Note: the error is actually in get_externals.bat, which is called by build.bat.

Since the checks are all against empty strings, perhaps we can use "IF NOT DEFINED PYTHON" instead? That should work as well, I think, and it'll save us from problems in the future if someone puts "]" in their username :)

Alas, "IF NOT DEFINED PYTHON" isn't working - as it's even more possible to get into a state where PYTHON="" than it is for a bracket to be in the python name.

Thus, the system would think it declared where we would have created it into an actual path otherwise.

Looks like the brackets are fine even in the bracket case Steve mentioned.

@echo off

if NOT DEFINED ABCDEF (
  echo "all good"
)

if NOT DEFINED ABCDE (
  echo "all good2"
)

set ABCDE=

if NOT DEFINED ABCDE (
  echo "sadness"
)

if [%ABCDE%]==[] (
  echo "all good3"
)

set ABCDE=]

if [%ABCDE%] NEQ [] (
  echo "all good4"
)

set ABCDE="]"

if [%ABCDE%] NEQ [] (
  echo "all good5"
)


>demo.bat
"all good"
"sadness"
"all good3"
"all good4"
"all good5"

Nevermind, the hold over issue was from another bit.

Updated the change request.

How long should I be waiting on review?

For this one you're probably waiting on me to get time. I try to find an hour or two each week, depending on what releases are going on, but it can be a little unpredictable.

Zachary could also review and merge if he gets time first. I don't think anyone else is likely to look at this.

New changeset 7ee88bf3e59493137a775368165c5c5fe1ed7f46 by Steve Dower (Jess) in branch 'master':
bpo-36245: Avoid problems when building in a directory containing spaces. (GH-12241)
https://github.com/python/cpython/commit/7ee88bf3e59493137a775368165c5c5fe1ed7f46

Fixed for 3.7 and master.

If it needs to go into 2.7 then someone will need to backport it manually.

New changeset b058a97c90c3144cc602b719483572916b3918bb by Miss Islington (bot) in branch '3.7':
bpo-36245: Avoid problems when building in a directory containing spaces. (GH-12241)
https://github.com/python/cpython/commit/b058a97c90c3144cc602b719483572916b3918bb

I did the 2.7 backport, and also fixed two more instances in that file.

Pretty sure my automerges won't work without a core dev review, so if someone wants to hit Approve and/or Merge for me, feel free.

New changeset bb89aa24cf71f9874d1d26f3a2440fefa0b6bbcc by Steve Dower in branch '2.7':
bpo-36245: Avoid problems when building in a directory containing spaces. (GH-12241)
https://github.com/python/cpython/commit/bb89aa24cf71f9874d1d26f3a2440fefa0b6bbcc

New changeset b95a79c928fc4a6135d91c0c553cb2a63cf15140 by Steve Dower in branch 'master':
bpo-36245: Fix more empty environment variable checks (GH-12592)
https://github.com/python/cpython/commit/b95a79c928fc4a6135d91c0c553cb2a63cf15140

New changeset 1ff04dcadfb57a8a8f61a6ea93292e8ae96dca4a by Miss Islington (bot) in branch '3.7':
bpo-36245: Fix more empty environment variable checks (GH-12592)
https://github.com/python/cpython/commit/1ff04dcadfb57a8a8f61a6ea93292e8ae96dca4a