how to add "wildcard-specific wildcard" via snakemake checkpoint - snakemake

Question

I can't find appropriate words to describe my need, please see the code.
My ideal workflow would do this:
I have known the categories that will be created during the workflow (cates)
I don't know how many files and what files would be created in each category (files)
For each category, rule create_file will be run first.
And then the checkpoint is triggered, I will know what files have been created for each category.
Then, for each file created in the create_file rule, a mock rule append_to_file_name take the file as input, and do the operation.
Files produced in create_file is wildcard specific so I call my need as "wildcard-specific" wildcard
cates=["A", "B"]
# pretend that you don't know about the files about to be created
files={
"A": ["a.txt", "b.txt"],
"B": ["c.txt", "d.txt"]
}
def get_append_to_file_output(wildcards):
files = glob_wildcards(f"{wildcards.cate}/{{file}}.txt").sample
appened = expand(f"{wildcards.cate}/{{file}}_append.txt", file = files)
return appened
rule all:
input:
get_append_to_file_output,
checkpoint create_file:
output: ddd=directory("{cate}"),
run:
from pathlib import Path
Path(output.ddd).mkdir(parents=True, exist_ok=True)
for file in files[wildcards.cate]:
Path(file).touch()
rule append_to_file_name:
input: ddd="{cate}",
output: "{cate}/{file}_append.txt",
run:
from pathlib import Path
Path(output[0]).touch()

Answer 1

cates=["A", "B"]
# pretend that you don't know about the files about to be created
files={
"A": ["a", "b"],
"B": ["c", "d"]
}
def get_append_to_file_output(wildcards):
cate_dir = checkpoints.create_file.get(**wildcards).output.ddd
files = glob_wildcards(f"{cate_dir}/{{file}}.txt").file
print(files)
appened = expand(f"results/append_filename/{wildcards.cate}/{{file}}_append.txt", file = files)
return appened
rule all:
input:
expand("results/flags/{cate}_aggregate.flag", cate=cates)
checkpoint create_file:
output:
ddd=directory("results/create_file/{cate}"),
run:
from pathlib import Path
Path(output.ddd).mkdir(parents=True, exist_ok=True)
for file in files[wildcards.cate]:
Path(f"{output.ddd}/{file}.txt").touch()
rule append_to_filename:
input:
ddd=rules.create_file.output.ddd
output:
appended="results/append_filename/{cate}/{file}_append.txt"
shell:
"cp {input.ddd}/{wildcards.file}.txt {output.appended}"
rule fake_aggregate:
input:
get_append_to_file_output
output:
touch("results/flags/{cate}_aggregate.flag")
I've solved this by adding a fake aggregating rule