Skip to content

Clarify that comparisons must have an environment variable and a string literal #2055

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
danyeaw wants to merge 1 commit into
base: main
Choose a base branch
from
+9 −5
Open

Clarify that comparisons must have an environment variable and a string literal #2055

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
14 changes: 9 additions & 5 deletions source/specifications/dependency-specifiers.rst
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -47,7 +47,9 @@ A dependency specification always specifies a distribution name. It may
include extras, which expand the dependencies of the named distribution to
enable optional features. The version installed can be controlled using
version limits, or giving the URL to a specific artifact to install. Finally
the dependency can be made conditional using environment markers.
the dependency can be made conditional using environment markers. Each
marker comparison must have an environment variable on one side and a string
literal on the other. Comparing two variables or two literals is not permitted.

Grammar
-------
Expand Down Expand Up @@ -93,8 +95,8 @@ environments::
'implementation_name' | 'implementation_version' |
'extra' | 'extras' | 'dependency_groups' # ONLY when defined by a containing layer
)
marker_var = wsp* (env_var | python_str)
marker_expr = marker_var marker_op marker_var
marker_expr = wsp* env_var marker_op python_str
| wsp* python_str marker_op env_var
| wsp* '(' marker wsp* ')'
marker_and = marker_expr wsp* 'and' marker_expr
| marker_expr
Expand Down Expand Up @@ -523,8 +525,8 @@ The complete parsley grammar::
'implementation_name' | 'implementation_version' |
'extra' | 'extras' | 'dependency_groups' # ONLY when defined by a containing layer
):varname -> lookup(varname)
marker_var = wsp* (env_var | python_str)
marker_expr = marker_var:l marker_op:o marker_var:r -> (o, l, r)
marker_expr = wsp* env_var:l marker_op:o wsp* python_str:r -> (o, l, r)
| wsp* python_str:l marker_op:o wsp* env_var:r -> (o, l, r)
| wsp* '(' marker:m wsp* ')' -> m
marker_and = marker_expr:l wsp* 'and' marker_expr:r -> ('and', l, r)
| marker_expr:m -> m
Expand Down Expand Up @@ -707,6 +709,8 @@ History
work. [#marker_comparison_logic]_
- January 2026: fix outdated references to other documents that were
inadvertently retained from :pep:`508`
- May 2026: Clarify that comparisons must have an environment variable and a
string literal and not two of one type.


References
Expand Down
Loading