ubuntu 14.04,pip无法升级matplotllib

当我尝试使用pip升级matplotlib时,它会输出:

Downloading/unpacking matplotlib from https://pypi.python.org/packages/source/m/matplotlib/matplotlib-1.4.0.tar.gz#md5=1daf7f2123d94745feac1a30b210940c
  Downloading matplotlib-1.4.0.tar.gz (51.2MB): 51.2MB downloaded
  Running setup.py (path:/tmp/pip_build_root/matplotlib/setup.py) egg_info for package matplotlib
    ============================================================================
    Edit setup.cfg to change the build options

    BUILDING MATPLOTLIB
                matplotlib: yes [1.4.0]
                    python: yes [2.7.6 (default, Mar 22 2014, 22:59:38)  [GCC
                            4.8.2]]
                  platform: yes [linux2]

    REQUIRED DEPENDENCIES AND EXTENSIONS
                     numpy: yes [version 1.8.2]
                       six: yes [using six version 1.7.3]
                  dateutil: yes [using dateutil version 2.2]
                   tornado: yes [using tornado version 4.0.1]
                 pyparsing: yes [using pyparsing version 2.0.2]
                     pycxx: yes [Couldn't import.  Using local copy.]
                    libagg: yes [pkg-config information for 'libagg' could not
                            be found. Using local copy.]
    Traceback (most recent call last):
      File "", line 17, in 
      File "/tmp/pip_build_root/matplotlib/setup.py", line 154, in 
        result = package.check()
      File "setupext.py", line 940, in check
        if 'No such file or directory\ngrep:' in version:
    TypeError: argument of type 'NoneType' is not iterable
    Complete output from command python setup.py egg_info:
    ============================================================================

Edit setup.cfg to change the build options



BUILDING MATPLOTLIB

            matplotlib: yes [1.4.0]

                python: yes [2.7.6 (default, Mar 22 2014, 22:59:38)  [GCC

                        4.8.2]]

              platform: yes [linux2]



REQUIRED DEPENDENCIES AND EXTENSIONS

                 numpy: yes [version 1.8.2]

                   six: yes [using six version 1.7.3]

              dateutil: yes [using dateutil version 2.2]

               tornado: yes [using tornado version 4.0.1]

             pyparsing: yes [using pyparsing version 2.0.2]

                 pycxx: yes [Couldn't import.  Using local copy.]

                libagg: yes [pkg-config information for 'libagg' could not

                        be found. Using local copy.]

Traceback (most recent call last):

  File "", line 17, in 

  File "/tmp/pip_build_root/matplotlib/setup.py", line 154, in 

    result = package.check()

  File "setupext.py", line 940, in check

    if 'No such file or directory\ngrep:' in version:

TypeError: argument of type 'NoneType' is not iterable

----------------------------------------
Cleaning up...
Command python setup.py egg_info failed with error code 1 in /tmp/pip_build_root/matplotlib
Storing debug log for failure in /home/username/.pip/pip.log

Exception information:
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/pip-1.5.6-py2.7.egg/pip/basecommand.py", line 122, in main
    status = self.run(options, args)
  File "/usr/local/lib/python2.7/dist-packages/pip-1.5.6-py2.7.egg/pip/commands/install.py", line 278, in run
    requirement_set.prepare_files(finder, force_root_egg_info=self.bundle, bundle=self.bundle)
  File "/usr/local/lib/python2.7/dist-packages/pip-1.5.6-py2.7.egg/pip/req.py", line 1229, in prepare_files
    req_to_install.run_egg_info()
  File "/usr/local/lib/python2.7/dist-packages/pip-1.5.6-py2.7.egg/pip/req.py", line 325, in run_egg_info
    command_desc='python setup.py egg_info')
  File "/usr/local/lib/python2.7/dist-packages/pip-1.5.6-py2.7.egg/pip/util.py", line 697, in call_subprocess
    % (command_desc, proc.returncode, cwd))
InstallationError: Command python setup.py egg_info failed with error code 1 in /tmp/pip_build_root/matplotlib