fix: require python >=3.7 again (the python 3.9 dependency was unnecessary)

setup.cfg

@@ -31,7 +31,7 @@ classifiers =
 zip_safe = False
 include_package_data = False
 packages = find:
-python_requires = >=3.9
+python_requires = >=3.7
 install_requires =
     appdirs
     configargparse

snakemake/__init__.py

@@ -4,9 +4,13 @@
 __license__ = "MIT"
 
 import sys
+from snakemake.common import MIN_PY_VERSION
 
-if sys.version_info < (3, 9):
-    raise ValueError("Snakemake requires at least Python 3.9.")
+if sys.version_info < MIN_PY_VERSION:
+    raise ValueError(
+        f"Snakemake requires at least Python {MIN_PY_VERSION}. Please ensure to execute it in a compatible Python environment.",
+        file=sys.stderr,
+    )
 
 import os
 import glob

snakemake/executors/__init__.py

@@ -20,6 +20,7 @@
 from functools import partial
 from collections import namedtuple
 import base64
+from typing import List
 import uuid
 import re
 import math
@@ -142,7 +143,7 @@ def get_resource_declarations(self, job: ExecutorJobInterface):
 
     def run_jobs(
         self,
-        jobs: list[ExecutorJobInterface],
+        jobs: List[ExecutorJobInterface],
         callback=None,
         submit_callback=None,
         error_callback=None,

snakemake/interfaces.py

@@ -5,14 +5,8 @@
 
 import sys
 
-# The typing API used here requires Python 3.9 or later and fails with unintuitive errors otherwise.
-if sys.version_info < (3, 9):
-    raise ValueError(
-        "Snakemake executor interface definition requires at least Python 3.9."
-    )
-
 from abc import ABC, abstractmethod
-from typing import Optional
+from typing import Optional, List, Dict
 
 
 class ExecutorJobInterface(ABC):
@@ -278,7 +272,7 @@ def latency_wait(self) -> int:
 
     @property
     @abstractmethod
-    def rerun_triggers(self) -> Optional[list[str]]:
+    def rerun_triggers(self) -> Optional[List[str]]:
         ...
 
     @property
@@ -328,12 +322,12 @@ def wrapper_prefix(self) -> Optional[str]:
 
     @property
     @abstractmethod
-    def overwrite_threads(self) -> dict[str, int]:
+    def overwrite_threads(self) -> Dict[str, int]:
         ...
 
     @property
     @abstractmethod
-    def overwrite_scatter(self) -> dict[str, int]:
+    def overwrite_scatter(self) -> Dict[str, int]:
         ...
 
     @property

test-environment.yml

@@ -2,7 +2,7 @@ channels:
   - conda-forge
   - bioconda
 dependencies:
-  - python >=3.9
+  - python >=3.7
   - yte
   - packaging
   - stopit

tests/test_conda_python_3_7_script/Snakefile

@@ -0,0 +1,7 @@
+rule random_python_conda_script:
+	output:
+		"version.txt"
+	conda:
+		"test_python_env.yaml"
+	script:
+		"test_script.py"

tests/test_conda_python_3_7_script/expected-results/version.txt

@@ -0,0 +1 @@
+3.7.12

tests/test_conda_python_3_7_script/test_python_env.yaml

@@ -0,0 +1,9 @@
+channels:
+  - conda-forge
+  - defaults
+dependencies:
+  - python =3.7.12
+  # add a dependency that is not used by Snakemake itself,
+  # to simulate the case where the Python script needs 3.7 and
+  # that dependency
+  - pillow =9.2

tests/test_conda_python_3_7_script/test_script.py

@@ -0,0 +1,5 @@
+import platform
+import PIL
+
+with open('version.txt', 'w') as f:
+    f.write(platform.python_version())

tests/tests.py

@@ -2023,6 +2023,10 @@ def test_conda_python_script():
     run(dpath("test_conda_python_script"), use_conda=True)
 
 
+def test_conda_python_3_7_script():
+    run(dpath("test_conda_python_3_7_script"), use_conda=True)
+
+
 def test_prebuilt_conda_script():
     sp.run("conda env create -f tests/test_prebuilt_conda_script/env.yaml", shell=True)
     run(dpath("test_prebuilt_conda_script"), use_conda=True)