Python version constraint.

.gitignore

+# Compiled python modules.
+*.pyc
+
+# Setuptools distribution folder.
+/dist/
+
+# Python egg metadata, regenerated from source files by setuptools.
+/*.egg-info
+
+# Backups
+*~

bin/split_merged.py

@@ -19,6 +19,9 @@ subgroups of those reads based on similarity.
 """
 
 import sys
+major, minor = sys.version_info[:2]
+if major < 3 or (major == 3 and minor < 8):
+    sys.exit("Need at least python 3.8\n")
 import logging
 from pathlib import Path
 import multiprocessing as mp
@@ -59,6 +62,7 @@ def main():
             pool.apply_async(
                 split_fasta, args=(
                     in_fname,
+                    # "Walrus" assignment expression introduced in Python 3.8
                     cell_id := in_fname.name[:-len("_merged.fasta")],
                     out_dir.join_path(cell_id)))
             for in_fname in in_fnames]

setup.py

@@ -39,7 +39,9 @@ setup(
     author="Blaise Li",
     author_email="blaise.li@normalesup.org",
     license="GNU GPLv3",
-    python_requires=">=3.4, <4",
+    # >=3.8 because using := in bin/split_merged.py
+    # Requirement could be relaxed to >=3.6 otherwise.
+    python_requires=">=3.8, <4",
     packages=find_packages(),
     scripts=["bin/split_merged.py"],
     #ext_modules = extensions,