add helper to check if path is below another

this is used in the Database manager

1 files changed, 9 insertions, 0 deletions

diff --git a/alot/db/utils.py b/alot/db/utils.py
index 45ee0db8..db8de0de 100644
--- a/alot/db/utils.py
+++ b/alot/db/utils.py
@@ -390,3 +390,12 @@ def encode_header(key, value):
     else:
         value = Header(value)
     return value
+
+def is_subdir_of(subpath, superpath):
+    #make both absolute    
+    superpath = os.path.realpath(superpath)
+    subpath = os.path.realpath(subpath)
+
+    #return true, if the common prefix of both is equal to directory
+    #e.g. /a/b/c/d.rst and directory is /a/b, the common prefix is /a/b
+    return os.path.commonprefix([subpath, superpath]) == superpath