snakemake input wildcards

Question

[ohu20a]

Please, can anybody explain what the **wildcards in the code below does. Also, I have come across both *wildcards and **wildcards, how are they different?

In this case, does **wildcards mean wildcards.sample?

def STAR_input(wildcards):
        if config["PE_or_SE"] == "SE":
            fq1="analysis/trimmed_data/{sample}_R1_trimmed.fq.gz".format(**wildcards)
            return fq1
        elif config["PE_or_SE"] == "PE":
            fq1 = "analysis/trimmed_data/{sample}_R1_val_1.fq.gz".format(**wildcards)
            fq2 = "analysis/trimmed_data/{sample}_R2_val_2.fq.gz".format(**wildcards)
            return [fq1,fq2]

[Pierre Lindenbaum]

**wildcards notation is for kwargs e.g: https://realpython.com/python-kwargs-and-args/

[Eric Lim]

def STAR_input(wildcards):
    # ** is named parameters
    # statements below all accomplish the same thing
    fq1="analysis/trimmed_data/{sample}_R1_trimmed.fq.gz".format(**wildcards)
    fq1="analysis/trimmed_data/{}_R1_trimmed.fq.gz".format(wildcards.sample)
    fq1=f"analysis/trimmed_data/{wildcards.sample}_R1_trimmed.fq.gz"

rule:
  input: STAR_input
  output: '{sample}.do.something.txt'