check_for_fat(): use subprocess.check_output to avoid dependency on Python 3.7

The text=... option for subprocess.Popen was added in Python 3.7 only
("text was added as a more readable alias for universal_newlines"), and
also "encoding" and "errors" were introduced in Python 3.6 only.
We don't want to stick to a specific py3k version, so let's try to
be as backwards compatible as possible.

Since we only need stdout of blkid let's switch to
subprocess.check_output instead.

Thanks: Florian Apolloner for review and feedback

diff --git a/grml2usb b/grml2usb
index b12cf88..7434901 100755 (executable)
--- a/grml2usb
+++ b/grml2usb
@@ -804,9 +804,7 @@ def check_for_fat(partition):
                 " (wrong UID/permissions or device/directory not present?)" % partition)
 
     try:
                 " (wrong UID/permissions or device/directory not present?)" % partition)
 
     try:

-        udev_info = subprocess.Popen(["/sbin/blkid", "-s", "TYPE", "-o", "value", partition],
-                                     stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True)
-        filesystem = udev_info.communicate()[0].rstrip()
+        filesystem = subprocess.check_output(["/sbin/blkid", "-s", "TYPE", "-o", "value", partition]).decode().rstrip()

 
         if filesystem != "vfat":
             raise CriticalException(
 
         if filesystem != "vfat":
             raise CriticalException(


@@ -814,7 +812,7 @@ def check_for_fat(partition):
                     "(Use --fat16 or run mkfs.vfat %s)" % (partition, partition))
 
     except OSError:
                     "(Use --fat16 or run mkfs.vfat %s)" % (partition, partition))
 
     except OSError:

-        raise CriticalException("Sorry, /sbin/blkid not available (install e2fsprogs?)")
+        raise CriticalException("Sorry, /sbin/blkid not available (install util-linux?)")

 
 
 def mkdir(directory):
 
 
 def mkdir(directory):