[IMPORTANT] Changes to python operation for Chromium developers

[Alex Ovsienko]

Hello Chromium developers,

This announcement might affect how your developer's machine operates, so please read it carefully.

We are announcing that we are creating python3 and python3.bat files in depot_tools that, if your Chromium developer setup is correct, will take over the system python3 references and point to CIPD provided Python currently at 3.11.8 version. This is done as a part of the effort to improve Python hermeticity and reproducibility, together with being able to control the Python version for all of our clients.

Now, if this change is something you would like to avoid, we provide an escape hatch: please set the environment variable DEPOT_TOOLS_PYTHON_BYPASS to anything but 0 and calling python3 will result in calling the system Python again.

If you have any questions or issues, please report them in cr/542430166.

--

• Alex Ovsienko

[Dirk Pranke]

Hi Alex,

In the past, we had concerns around (a) overriding what the system might expect the default version of python to be (particularly on Mac) and (b) making it too difficult for a user to control the version of python they themselves wanted; to address the hermeticity and versioning concerns we provided `depot_tools/python-bin` and/or recommended people use `vpython`. 

Your note sounds like a change (or even reversal) of that policy. Is that correct? I'm curious what, if anything, changed that led to this decision.

-- Dirk

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[Nico Weber]

On Tue, Aug 4, 2026 at 1:16 PM Dirk Pranke <dpr...@chromium.org> wrote:

Hi Alex,

In the past, we had concerns around (a) overriding what the system might expect the default version of python to be (particularly on Mac) and (b) making it too difficult for a user to control the version of python they themselves wanted; to address the hermeticity and versioning concerns we provided `depot_tools/python-bin` and/or recommended people use `vpython`. 

Your note sounds like a change (or even reversal) of that policy. Is that correct? I'm curious what, if anything, changed that led to this decision.

We're not planning to change what `python3` when run manually does, only which python the build calls. We want to have a hermetic python binary that's versioned with src.git, like we handle other compilers (clang, rust, node I think, etc). crbug.com/537680330 is the tracking bug, it has more details.

 

To view this discussion visit https://groups.google.com/a/chromium.org/d/msgid/chromium-dev/CALyq14_ciGPPH_vTXt_YkLvtQF4DvdNwkujqnDS5sQt7eBuCQw%40mail.gmail.com.

[Dirk Pranke]

On Wed, Aug 5, 2026 at 4:41 PM Nico Weber <tha...@chromium.org> wrote:

On Tue, Aug 4, 2026 at 1:16 PM Dirk Pranke <dpr...@chromium.org> wrote:

Hi Alex,

In the past, we had concerns around (a) overriding what the system might expect the default version of python to be (particularly on Mac) and (b) making it too difficult for a user to control the version of python they themselves wanted; to address the hermeticity and versioning concerns we provided `depot_tools/python-bin` and/or recommended people use `vpython`. 

Your note sounds like a change (or even reversal) of that policy. Is that correct? I'm curious what, if anything, changed that led to this decision.

We're not planning to change what `python3` when run manually does, only which python the build calls. We want to have a hermetic python binary that's versioned with src.git, like we handle other compilers (clang, rust, node I think, etc). crbug.com/537680330 is the tracking bug, it has more details.

That is not what Alex's note says, and he seemed to confirm my understanding in a reply off-thread.

Regardless, I have commented on the bug and we can continue the discussion there for now if you'd rather it be off-list.

-- Dirk