move git head functionality to function in util.py

gallery_dl/__init__.py

@@ -118,25 +118,15 @@ def main():
             config.set(("output",), "mode", "null")
         elif args.loglevel <= logging.DEBUG:
             import platform
-            import subprocess
-            import os.path
             import requests
 
             extra = ""
             if getattr(sys, "frozen", False):
                 extra = " - Executable"
             else:
-                try:
+                git_head = util.git_head()
-                    out, err = subprocess.Popen(
+                if git_head:
-                        ("git", "rev-parse", "--short", "HEAD"),
+                    extra = " - Git HEAD: " + git_head
-                        stdout=subprocess.PIPE,
-                        stderr=subprocess.PIPE,
-                        cwd=os.path.dirname(os.path.abspath(__file__)),
-                    ).communicate()
-                    if out and not err:
-                        extra = " - Git HEAD: " + out.decode().rstrip()
-                except (OSError, subprocess.SubprocessError):
-                    pass
 
             log.debug("Version %s%s", __version__, extra)
             log.debug("Python %s - %s",

gallery_dl/util.py

@@ -19,6 +19,7 @@ import binascii
 import datetime
 import functools
 import itertools
+import subprocess
 import urllib.parse
 from http.cookiejar import Cookie
 from email.utils import mktime_tz, parsedate_tz
@@ -273,6 +274,22 @@ Response Headers
         fp.write(response.content)
 
 
+@functools.lru_cache(maxsize=None)
+def git_head():
+    try:
+        out, err = subprocess.Popen(
+            ("git", "rev-parse", "--short", "HEAD"),
+            stdout=subprocess.PIPE,
+            stderr=subprocess.PIPE,
+            cwd=os.path.dirname(os.path.abspath(__file__)),
+        ).communicate()
+        if out and not err:
+            return out.decode().rstrip()
+    except (OSError, subprocess.SubprocessError):
+        pass
+    return None
+
+
 def expand_path(path):
     """Expand environment variables and tildes (~)"""
     if not path: