Why does setting `wildcard_constraints` in a snakefile prevent the deletion of files marked `temp`?

Consider the following snakefile: ``` NUMS = ["1", "2"] #wildcard_constraints: # num="\d+" rule all: input: "all_text.txt" rule generate_text: output: text_file = temp("text_{num}.txt") shell: """ echo "test" > {output.text_file} """ rule gather_results: input: expand("text_{num}.txt", num=NUMS) output: "all_text.txt" shell: """ cat {input} > {output} """ ``` If I uncomment the `wildcard_constraints` section, the files marked `temp` are not deleted. What could be the cause of this ? More tests Putting `wildcard_constraints` in the rule: ``` rule generate_text: output: text_file = temp("text_{num}.txt") wildcard_constraints: num="\d+" shell: """ echo "test" > {output.text_file} """ ``` This has the same effect: `temp` files are not deleted. Putting the wildcard constraint in the output file name of the `generate_text` rule: ``` rule generate_text: output: text_file = temp("text_{num,\d+}.txt") shell: """ echo "test" > {output.text_file} """ ``` In this case, `temp` files are deleted as expected. Putting the constraint in the input filename of the `gather_results` rule: ``` rule gather_results: input: expand("text_{num,\d+}.txt", num=NUMS) output: "all_text.txt" shell: """ cat {input} > {output} """ ``` This results in an error: WildcardError in line 20 of /tmp/Snakefile: No values given for wildcard 'num,\d+'. File "/tmp/Snakefile", line 20, in I suspect this is due to the use of `expand`.