Implement module for interfacing with rust-qtlreaper

Issue:
https://github.com/genenetwork/gn-gemtext-threads/blob/main/topics/gn1-migration-to-gn2/clustering.gmi

* gn3/computations/heatmap.py: move `generate_traits_file` function to new
  module
* gn3/computations/qtlreaper.py: new module to interface with the
  `rust-qtlreaper` utility.
* gn3/settings.py: Provide setting for the path to the `rust-qtlreaper`
  utility
* qtlfilesexport.py: Move `random_string` function to new module. Update to
  use functions in new module.

  Provide a module with functions to be used to interface with
  `rust-qtlreaper`. This module essentially contains all the functions that
  are needed to build the files needed for, and to run the qtlreaper utility.

2 files changed, 88 insertions, 8 deletions

diff --git a/gn3/computations/heatmap.py b/gn3/computations/heatmap.py
index 3e96ed2..dcd64b1 100644
--- a/gn3/computations/heatmap.py
+++ b/gn3/computations/heatmap.py
@@ -230,11 +230,3 @@ def retrieve_strains_and_values(orders, strainlist, traits_data_list):
         values = []
 
     return rets
-
-def generate_traits_file(strains, trait_values, traits_filename):
-    header = "Traits\t{}\n".format("\t".join(strains))
-    data = [header] + [
-        "T{}\t{}\n".format(i+1, "\t".join([str(i) for i in t]))
-        for i,t in enumerate(trait_values)]
-    with open(traits_filename, "w") as outfile:
-        outfile.writelines(data)
diff --git a/gn3/computations/qtlreaper.py b/gn3/computations/qtlreaper.py
new file mode 100644
index 0000000..49d363b
--- /dev/null
+++ b/gn3/computations/qtlreaper.py
@@ -0,0 +1,88 @@
+"""
+This module contains functions to interact with the `qtlreaper` utility for
+computation of QTLs.
+"""
+import os
+import random
+import string
+import subprocess
+from gn3.settings import TMPDIR, REAPER_COMMAND
+
+def random_string(length):
+    """Generate a random string of length `length`."""
+    return "".join(
+        random.choices(
+            string.ascii_letters + string.digits, k=length))
+
+def generate_traits_file(strains, trait_values, traits_filename):
+    """
+    Generate a traits file for use with `qtlreaper`.
+
+    PARAMETERS:
+    strains: A list of strains to use as the headers for the various columns.
+    trait_values: A list of lists of values for each trait and strain.
+    traits_filename: The tab-separated value to put the values in for
+        computation of QTLs.
+    """
+    header = "Traits\t{}\n".format("\t".join(strains))
+    data = [header] + [
+        "T{}\t{}\n".format(i+1, "\t".join([str(i) for i in t]))
+        for i, t in enumerate(trait_values)]
+    with open(traits_filename, "w") as outfile:
+        outfile.writelines(data)
+
+def create_output_directory(path: str):
+    """Create the output directory at `path` if it does not exist."""
+    try:
+        os.mkdir(path)
+    except OSError:
+        pass
+
+def run_reaper(
+        genotype_filename: str, traits_filename: str,
+        other_options: tuple = ("--n_permutations", 1000),
+        separate_nperm_output: bool = False,
+        output_dir: str = TMPDIR):
+    """
+    Run the QTLReaper command to compute the QTLs.
+
+    PARAMETERS:
+    genotype_filename: The complete path to a genotype file to use in the QTL
+        computation.
+    traits_filename: A path to a file previously generated with the
+        `generate_traits_file` function in this module, to be used in the QTL
+        computation.
+    other_options: Other options to pass to the `qtlreaper` command to modify
+        the QTL computations.
+    separate_nperm_output: A flag indicating whether or not to provide a
+        separate output for the permutations computation. The default is False,
+        which means by default, no separate output file is created.
+    output_dir: A path to the directory where the outputs are put
+
+    RETURNS:
+    The function returns a tuple of the main output file, and the output file
+    for the permutation computations. If the `separate_nperm_output` is `False`,
+    the second value in the tuple returned is `None`.
+
+    RAISES:
+    The function will raise a `subprocess.CalledProcessError` exception in case
+    of any errors running the `qtlreaper` command.
+    """
+    create_output_directory(output_dir)
+    output_filename = "{}/qtlreaper/main_output_{}.txt".format(
+        output_dir, random_string(10))
+    output_list = ["--main_output", output_filename]
+    if separate_nperm_output:
+        permu_output_filename = "{}/qtlreaper/permu_output_{}.txt".format(
+            output_dir, random_string(10))
+        output_list = output_list + ["--permu_output", permu_output_filename]
+    else:
+        permu_output_filename = None
+
+    command_list = [
+        REAPER_COMMAND, "--geno", genotype_filename,
+        *other_options, # this splices the `other_options` list here
+        "--traits", traits_filename, "--main_output", output_filename]
+
+    subprocess.run(command_list, check=True)
+    return (output_filename, permu_output_filename)