Make the modem manager check more pythonic

lib/python/qmk/cli/doctor.py

@@ -21,17 +21,17 @@ def main(cli):
         * [ ] Compile a trivial program with each compiler
         * [ ] Check for udev entries on linux
     """
+    cli.log.info('QMK Doctor is checking your environment.')
 
+    # Make sure the basic CLI tools we need are available and can be executed.
     binaries = ['dfu-programmer', 'avrdude', 'dfu-util', 'avr-gcc', 'arm-none-eabi-gcc']
     binaries += glob('bin/qmk-*')
-
-    cli.log.info('QMK Doctor is checking your environment')
-
     ok = True
+
     for binary in binaries:
         res = shutil.which(binary)
         if res is None:
-            cli.log.error("{fg_red}QMK can't find %s in your path", binary)
+            cli.log.error("{fg_red}QMK can't find %s in your path.", binary)
             ok = False
         else:
             try:
@@ -40,20 +40,36 @@ def main(cli):
                 cli.log.error("{fg_red}Can't run `%s --version`", binary)
                 ok = False
 
+    # Determine our OS and run platform specific tests
     OS = platform.system()
+
     if OS == "Darwin":
-        cli.log.info("Detected {fg_cyan}macOS")
+        cli.log.info("Detected {fg_cyan}macOS.")
+
     elif OS == "Linux":
-        cli.log.info("Detected {fg_cyan}linux")
+        cli.log.info("Detected {fg_cyan}Linux.")
         if shutil.which('systemctl'):
-            test = 'systemctl list-unit-files | grep enabled | grep -i ModemManager'
-            if os.system(test) == 0:
-                cli.log.warn("{bg_yellow}Detected modem manager. Please disable it if you are using Pro Micros")
+            mm_check = subprocess.run(['systemctl', 'list-unit-files'], stdout=subprocess.PIPE, stderr=subprocess.PIPE, timeout=10)
+            if mm_check.returncode == 0:
+                mm = True
+                for line in mm_check.stdout.split('\n'):
+                    if 'ModemManager' in line and 'enabled' in line:
+                        mm = False
+
+                if mm:
+                    cli.log.warn("{bg_yellow}Detected ModemManager. Please disable it if you are using a Pro-Micro.")
+
+            else:
+                cli.log.error('{bg_red}Could not run `systemctl list-unit-files`:')
+                cli.log.error(mm_check.stderr)
+
         else:
             cli.log.warn("Can't find systemctl to check for ModemManager.")
-    else:
-        cli.log.info("Assuming {fg_cyan}Windows")
 
+    else:
+        cli.log.info("Assuming {fg_cyan}Windows.")
+
+    # Report a summary of our findings to the user
     if ok:
         cli.log.info('{fg_green}QMK is ready to go')
     else: