pip will ignore environment makers in combination with "extra-index-url"

[loscrossos]

Description

Summary

Problem

When installing packages from requirements txt pip will ignore environment makers in combination with "extra-index-url".

this requirements.txt ignores OS constraints on indexes even though environment markers are defined in PEP508/PyPa Spec and it seems no exception is made for index elements. There fore i would expect this file to be compliant

--extra-index-url=https://download.pytorch.org/whl/nightly/cpu ; sys_platform  == 'darwin'
--extra-index-url=https://download.pytorch.org/whl/cu129 ; sys_platform  != 'darwin'
torch==2.9.0 ; sys_platform  != 'darwin'
torch ; sys_platform  == 'darwin'
torchvision
torchaudio

intended is on mac to instal the nightly CPU and on everything that is not mac (Linux/windows) the CUDA version of pytorch using the extra index.

what happens instead

-pip will ignore the markers on the first two lines, but it process the indexes and thus and concatenate the indexes one after another (which makes sense as those are extra indexes)
-pip will obey the markers on the packages (e,g, torch==2.9.0 ; sys_platform != 'darwin')

pips output when running the first example (e.g. on Macos):

Looking in indexes: https://pypi.org/simple, https://download.pytorch.org/whl/nightly/cpu, https://download.pytorch.org/whl/cu129
Ignoring torch: markers 'sys_platform != "darwin"' don't match your environment

it installs the normal release torch==2.9.0 (not the nightly from pytorch).

is this intended behavior? or a bug?

the documentation (as far as i read it) does not make an exception for environment markers (sys_platform, os_name, etc).

markers work otherwise normally as expected on normal package names.

Expected behavior

No response

pip version

25.3

Python version

3.13, 3.12, 3.10

OS

MacOS, Linux, Windows

How to Reproduce

save this file as requirements.txt

--extra-index-url=https://download.pytorch.org/whl/nightly/cpu ; sys_platform  == 'darwin'
--extra-index-url=https://download.pytorch.org/whl/cu129 ; sys_platform  != 'darwin'
torch==2.9.0 ; sys_platform  != 'darwin'
torch ; sys_platform  == 'darwin'
torchvision
torchaudio

install with pip on macOS.

Output

$ pip install -r requirements.txt
Looking in indexes: https://pypi.org/simple, https://download.pytorch.org/whl/nightly/cpu, https://download.pytorch.org/whl/cu129
Ignoring torch: markers 'sys_platform != "darwin"' don't match your environment
Collecting torch (from -r uvtest.txt (line 4))
Downloading torch-2.9.0-cp313-none-macosx_11_0_arm64.whl.metadata (30 kB)
Collecting torchvision (from -r uvtest.txt (line 5))
Downloading torchvision-0.24.0-cp313-cp313-macosx_12_0_arm64.whl.metadata (5.9 kB)
Collecting torchaudio (from -r uvtest.txt (line 6))
Downloading torchaudio-2.9.0-cp313-cp313-macosx_12_0_arm64.whl.metadata (6.9 kB)
Collecting filelock (from torch->-r uvtest.txt (line 4))
Downloading https://download.pytorch.org/whl/nightly/filelock-3.20.0-py3-none-any.whl.metadata (2.1 kB)
Collecting typing-extensions>=4.10.0 (from torch->-r uvtest.txt (line 4))
Downloading https://download.pytorch.org/whl/typing_extensions-4.15.0-py3-none-any.whl.metadata (3.3 kB)
Collecting setuptools (from torch->-r uvtest.txt (line 4))
Downloading setuptools-80.9.0-py3-none-any.whl.metadata (6.6 kB)
Collecting sympy>=1.13.3 (from torch->-r uvtest.txt (line 4))
Downloading https://download.pytorch.org/whl/sympy-1.14.0-py3-none-any.whl.metadata (12 kB)
Collecting networkx>=2.5.1 (from torch->-r uvtest.txt (line 4))
Downloading https://download.pytorch.org/whl/networkx-3.5-py3-none-any.whl.metadata (6.3 kB)
Collecting jinja2 (from torch->-r uvtest.txt (line 4))
Downloading https://download.pytorch.org/whl/jinja2-3.1.6-py3-none-any.whl.metadata (2.9 kB)
Collecting fsspec>=0.8.5 (from torch->-r uvtest.txt (line 4))
Downloading https://download.pytorch.org/whl/fsspec-2025.9.0-py3-none-any.whl.metadata (10 kB)
Collecting numpy (from torchvision->-r uvtest.txt (line 5))
Downloading https://download.pytorch.org/whl/nightly/numpy-2.3.4-cp313-cp313-macosx_14_0_arm64.whl.metadata (62 kB)
Collecting pillow!=8.3.*,>=5.3.0 (from torchvision->-r uvtest.txt (line 5))
Downloading https://download.pytorch.org/whl/nightly/pillow-12.0.0-cp313-cp313-macosx_11_0_arm64.whl.metadata (8.8 kB)
Collecting mpmath<1.4,>=1.1.0 (from sympy>=1.13.3->torch->-r uvtest.txt (line 4))
Downloading https://download.pytorch.org/whl/mpmath-1.3.0-py3-none-any.whl (536 kB)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 536.2/536.2 kB 6.1 MB/s 0:00:00
Collecting MarkupSafe>=2.0 (from jinja2->torch->-r uvtest.txt (line 4))
Downloading markupsafe-3.0.3-cp313-cp313-macosx_11_0_arm64.whl.metadata (2.7 kB)
Downloading torch-2.9.0-cp313-none-macosx_11_0_arm64.whl (74.5 MB)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 74.5/74.5 MB 6.9 MB/s 0:00:10
Downloading torchvision-0.24.0-cp313-cp313-macosx_12_0_arm64.whl (1.9 MB)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 1.9/1.9 MB 6.8 MB/s 0:00:00
Downloading torchaudio-2.9.0-cp313-cp313-macosx_12_0_arm64.whl (809 kB)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 809.1/809.1 kB 5.8 MB/s 0:00:00
Downloading https://download.pytorch.org/whl/fsspec-2025.9.0-py3-none-any.whl (199 kB)
Downloading https://download.pytorch.org/whl/networkx-3.5-py3-none-any.whl (2.0 MB)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 2.0/2.0 MB 6.4 MB/s 0:00:00
Downloading https://download.pytorch.org/whl/nightly/pillow-12.0.0-cp313-cp313-macosx_11_0_arm64.whl (4.7 MB)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 4.7/4.7 MB 7.2 MB/s 0:00:00
Downloading https://download.pytorch.org/whl/sympy-1.14.0-py3-none-any.whl (6.3 MB)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 6.3/6.3 MB 7.0 MB/s 0:00:00
Downloading https://download.pytorch.org/whl/typing_extensions-4.15.0-py3-none-any.whl (44 kB)
Downloading https://download.pytorch.org/whl/nightly/filelock-3.20.0-py3-none-any.whl (16 kB)
Downloading https://download.pytorch.org/whl/jinja2-3.1.6-py3-none-any.whl (134 kB)
Downloading markupsafe-3.0.3-cp313-cp313-macosx_11_0_arm64.whl (12 kB)
Downloading https://download.pytorch.org/whl/nightly/numpy-2.3.4-cp313-cp313-macosx_14_0_arm64.whl (5.1 MB)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 5.1/5.1 MB 6.7 MB/s 0:00:00
Downloading setuptools-80.9.0-py3-none-any.whl (1.2 MB)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 1.2/1.2 MB 6.9 MB/s 0:00:00
Installing collected packages: mpmath, typing-extensions, sympy, setuptools, pillow, numpy, networkx, MarkupSafe, fsspec, filelock, jinja2, torch, torchvision, torchaudio
Successfully installed MarkupSafe-3.0.3 filelock-3.20.0 fsspec-2025.9.0 jinja2-3.1.6 mpmath-1.3.0 networkx-3.5 numpy-2.3.4 pillow-12.0.0 setuptools-80.9.0 sympy-1.14.0 torch-2.9.0 torchaudio-2.9.0 torchvision-0.24.0 typing-extensions-4.15.0

Code of Conduct

• I agree to follow the PSF Code of Conduct.

[ichard26]

requirements.txt is not really a standardized format, it's actually a custom pip format. It seems standard since everyone uses it, but that's because it has existed for forever (and well, pip used to be the only installer in town).

PEP 508 or the Dependency specifier specification (used pretty much everywhere now) was inspired by pip's existing requirements.txt, but it only codified the package specifier syntax. As noted in the spec, it does not cover the CLI handling since that's tool specific.

The language defined is a compact line based format which is already in widespread use in pip requirements files, though we do not specify the command line option handling that those files permit.

(emphasis my own). Thus, pip doesn't violate the specification by ignoring environment markers for lines containing command line arguments.

This sounds like a reasonable feature request, although honestly, we've mostly stopped innovating the requirements.txt format so don't hold your breath waiting for support to be added. We generally focus our efforts on expanding/refining our support for standardized features first (like the pylock standard).

[notatallshaw]

My gut reaction is pip should deprecate markers on options and eventually throw an error.

Given they're already ignored they probably weren't intentional.