Does Snakefile location matter? - snakemake

Question

I am absolute beginner to snakemake. I am building a pipeline as I learn. My question is if the Snakefile is placed with data file that I want to process an NameError: occurs but if I move the Snakefile to a parent directory and edit the path information of input: and output: the code works. what am I missing?
rule sra_convert:
input:
"rna/{id}.sra"
output:
"rna/fastq/{id}.fastq"
shell:
"fastq-dump {input} -O {output}"
above code works fine when I run with
snakemake -p rna/fastq/SRR873382.fastq
However, if I move the file to "rna" directory where the SRR873382.sra file is and edit the code as below
rule sra_convert:
input:
"{id}.sra"
output:
"fastq/{id}.fastq"
message:
"Converting from {id}.sra to {id}.fastq"
shell:
"fastq-dump {input} -O {output}"
and run
snakemake -p fastq/SRR873382.fastq
I get the following error
Building DAG of jobs...
Job counts:
count jobs
1 sra_convert
1
RuleException in line 7 of /home/sarc/Data/rna/Snakefile:
NameError: The name 'id' is unknown in this context. Please make sure that you defined that variable. Also note that braces not used for variable access have to be escaped by repeating them, i.e. {{print $1}}
Solution
rule sra_convert:
input:
"{id}.sra"
output:
"fastq/{id}.fastq"
message:
"Converting from {wildcards.id}.sra to {wildcards.id}.fastq"
shell:
"fastq-dump {input} -O {output}"
above code runs fine without error

Answer 1

I believe that the best source that answers your actual question is:
https://snakemake.readthedocs.io/en/stable/snakefiles/rules.html#wildcards
If the rule’s output matches a requested file, the substrings matched
by the wildcards are propagated to the input files and to the variable
wildcards, that is here also used in the shell command. The wildcards
object can be accessed in the same way as input and output, which is
described above.