upgrade samba 4 alpha9 to samba 4 alpha 11-error

[hesam mohamadian]

hi i installed samba4 alpha 9  and i want to upgrade to samba4 alpha11 , i
get samba4 alpha11 from git and for upgrading i do this :
./scripting/bin/upgradeprovision --full -s
/usr/local/backupprovision/etc/smb.conf

Traceback (most recent call last):
  File "./scripting/bin/upgradeprovision", line 36, in <module>
    import ldb
ImportError: No module named ldb

what should i do , anybody can help ?