Snakemake Log参数配置报错：log关键字后需加冒号

Let's break down and fix the issues in your Snakefile that are triggering the syntax error and potential execution problems:

1. Correct the Log Block Syntax #

The error Colon expected after keyword log stems from how you defined the log entry. In Snakemake, the log block follows strict syntax rules:

• For a single log file, you can directly specify the path without using a = key-value assignment.
• If you need named keys for multiple log files (for later reference), use dictionary-style formatting with colons (not equals signs), and avoid using log as a key name (it conflicts with the block's own name).

For your single HTML log, simplify the log block to:

log: WORK_DIR + "/logs/fastp/{sample}.html"

If you prefer a named key for clarity (useful if you add more logs later), adjust it to:

log:
    html = WORK_DIR + "/logs/fastp/{sample}.html"

2. Fix the Shell Command Line Continuation #

Your shell command has a space after the backslash (\ -h), which breaks the line continuation. The backslash must be the last character on the line to properly signal that the command continues on the next line.

Full Corrected Snakefile #

Here's the revised code with both fixes applied:

include: 'config.py'
rule all:
    input: expand(WORK_DIR +"/trimmed/TFB{sample}_R{read_no}.fastq.gz.good", sample=SAMPLE_TFB ,read_no=['1', '2'])
rule fastp:
    input:
        R1= SAMPLES_DIR + "/TFB{sample}_R1.fastq.gz",
        R2= SAMPLES_DIR + "/TFB{sample}_R2.fastq.gz"
    output:
        R1out= WORK_DIR + "/trimmed/TFB{sample}_R1.fastq.gz.good",
        R2out= WORK_DIR + "/trimmed/TFB{sample}_R2.fastq.gz.good"
    log: WORK_DIR + "/logs/fastp/{sample}.html"
    shell: """
        fastp -i {input.R1} -I {input.R2} -o {output.R1out} -O {output.R2out} \
        -h {log}
    """

Optional: Auto-Create Log Directory #

To avoid errors if the logs/fastp directory doesn't exist, add a command to create it before running fastp:

shell: """
    mkdir -p $(dirname {log}) && \
    fastp -i {input.R1} -I {input.R2} -o {output.R1out} -O {output.R2out} \
    -h {log}
"""

内容的提问来源于stack exchange，提问作者Leandro Boralli