nested for loop in f-string

[sneuensc]

Snakemake version
Bug in latest versions. Tested versions 8.7.0 and 8.11.3.
Works in version 7.18.2

Describe the bug
I often use nested 'for' loops to create a list (outside of a rule). This works fine, but if the loop is placed WITHIN an f-string it does not work with the latest versions of snakemake. Before version 8 it was working.

Logs
$ snakemake -j1
SyntaxError in file Snakefile, line 6:
invalid syntax. Perhaps you forgot a comma? (Snakefile, line 6)

Minimal example

works for both versions

a = [(x, y) for x in [1,2,3] for y in [3,1,4]]
print(f"works for both versions: {a}")

works for older versions only

print(f"works only in old version: {[(x, y) for x in [1,2,3] for y in [3,1,4]]}")

[cmeesters]

Snakemake states an error in your Snakefile. Please provide a minimal example to produce your error using the current version of Snakemake.

[Hocnonsense]

Yes... This is indeed a bug that caused by f-string.

In brief, python will split each 'word' in fstring such as f"works only in old version: {, [, (, x, ,, y, ), for, x, in ...
however, the space between each word are missed. Snakemake read smk file using python parser, and this is difficult to keep it.

This bug will be fixed in the future, but it is also better to use f-string in a more gentle way :)