I can't install pyusb through macports

[心如烛光]

Hi,everybody.
    I wanna install py27-pyusb into my OSX(lion 10.7.4) through macports. But I meet some errors.And I wanna know that what cause these errors and how can I fix it?Thanks for your help!
I input:sudo port install py27-pyusb-devel
then it responds:
--->  Computing dependencies for py27-pyusb-devel
--->  Dependencies to be installed: python27
--->  Activating python27 @2.7.3_0
Error: org.macports.activate for port python27 returned: Image error: /Applications/MacPorts/Python 2.7/Build Applet.app/Contents/Info.plist already exists and does not belong to a registered port.  Unable to activate port python27. Use 'port -f activate python27' to force the activation.
Error: Failed to install python27
Please see the log file for port python27 for details:
    /opt/local/var/macports/logs/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_lang_python27/python27/main.log
Error: The following dependencies were not installed: python27
To report a bug, follow the instructions in the guide:
    http://guide.macports.org/#project.tickets
Error: Processing of port py27-pyusb-devel failed
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