Try --

   yum install freetype-devel

This installed successfully.

Or as a shortcut to get all of the build dependencies installed:

   yum-builddep python-matplotlib

This ended with:

(mandala)[webalert@localhost ~]$ sudo yum-builddep python-matplotlib
[sudo] password for webalert: 
Loaded plugins: fastestmirror, refresh-packagekit
Loading mirror speeds from cached hostfile
 * base: centos.mirror.ca.planethoster.net
 * extras: mirror.science.uottawa.ca
 * rpmforge: mirror.team-cymru.org
 * updates: centos.mirror.ca.planethoster.net
Checking for new repos for mirrors
No source RPM found for python-matplotlib-0.99.1.2-1.el6.x86_64
No uninstalled build requires

Still running into the error:

gcc -pthread -fno-strict-aliasing -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2
-fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic
-D_GNU_SOURCE -fPIC -fwrapv -DNDEBUG -O2 -g -pipe -Wall
-Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector
--param=ssp-buffer-size=4 -m64 -mtune=generic -D_GNU_SOURCE -fPIC -fwrapv
-fPIC -DPY_ARRAY_UNIQUE_SYMBOL=MPL_ARRAY_API -DPYCXX_ISO_CPP_LIB=1
-I/usr/local/include -I/usr/include
-I/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include
-I/usr/local/include -I/usr/include -I.
-I/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include
-Isrc -Iagg24/include -I. -I/usr/include/python2.6 -c
agg24/src/agg_trans_affine.cpp -o
build/temp.linux-x86_64-2.6/agg24/src/agg_trans_affine.o

gcc -pthread -fno-strict-aliasing -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2
-fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic
-D_GNU_SOURCE -fPIC -fwrapv -DNDEBUG -O2 -g -pipe -Wall
-Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector
--param=ssp-buffer-size=4 -m64 -mtune=generic -D_GNU_SOURCE -fPIC -fwrapv
-fPIC -DPY_ARRAY_UNIQUE_SYMBOL=MPL_ARRAY_API -DPYCXX_ISO_CPP_LIB=1
-I/usr/local/include -I/usr/include
-I/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include
-I/usr/local/include -I/usr/include -I.
-I/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include
-Isrc -Iagg24/include -I. -I/usr/include/python2.6 -c
agg24/src/agg_image_filters.cpp -o
build/temp.linux-x86_64-2.6/agg24/src/agg_image_filters.o

gcc -pthread -fno-strict-aliasing -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2
-fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic
-D_GNU_SOURCE -fPIC -fwrapv -DNDEBUG -O2 -g -pipe -Wall
-Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector
--param=ssp-buffer-size=4 -m64 -mtune=generic -D_GNU_SOURCE -fPIC -fwrapv
-fPIC -DPY_ARRAY_UNIQUE_SYMBOL=MPL_ARRAY_API -DPYCXX_ISO_CPP_LIB=1
-I/usr/local/include -I/usr/include
-I/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include
-I/usr/local/include -I/usr/include -I.
-I/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include
-Isrc -Iagg24/include -I. -I/usr/include/python2.6 -c
agg24/src/agg_bezier_arc.cpp -o
build/temp.linux-x86_64-2.6/agg24/src/agg_bezier_arc.o

gcc -pthread -fno-strict-aliasing -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2
-fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic
-D_GNU_SOURCE -fPIC -fwrapv -DNDEBUG -O2 -g -pipe -Wall
-Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector
--param=ssp-buffer-size=4 -m64 -mtune=generic -D_GNU_SOURCE -fPIC -fwrapv
-fPIC -DPY_ARRAY_UNIQUE_SYMBOL=MPL_ARRAY_API -DPYCXX_ISO_CPP_LIB=1
-I/usr/local/include -I/usr/include
-I/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include
-I/usr/local/include -I/usr/include -I.
-I/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include
-Isrc -Iagg24/include -I. -I/usr/include/python2.6 -c CXX/cxxsupport.cxx -o
build/temp.linux-x86_64-2.6/CXX/cxxsupport.o

gcc -pthread -fno-strict-aliasing -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2
-fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic
-D_GNU_SOURCE -fPIC -fwrapv -DNDEBUG -O2 -g -pipe -Wall
-Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector
--param=ssp-buffer-size=4 -m64 -mtune=generic -D_GNU_SOURCE -fPIC -fwrapv
-fPIC -DPY_ARRAY_UNIQUE_SYMBOL=MPL_ARRAY_API -DPYCXX_ISO_CPP_LIB=1
-I/usr/local/include -I/usr/include
-I/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include
-I/usr/local/include -I/usr/include -I.
-I/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include
-Isrc -Iagg24/include -I. -I/usr/include/python2.6 -c CXX/cxx_extensions.cxx
-o build/temp.linux-x86_64-2.6/CXX/cxx_extensions.o

gcc -pthread -fno-strict-aliasing -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2
-fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic
-D_GNU_SOURCE -fPIC -fwrapv -DNDEBUG -O2 -g -pipe -Wall
-Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector
--param=ssp-buffer-size=4 -m64 -mtune=generic -D_GNU_SOURCE -fPIC -fwrapv
-fPIC -DPY_ARRAY_UNIQUE_SYMBOL=MPL_ARRAY_API -DPYCXX_ISO_CPP_LIB=1
-I/usr/local/include -I/usr/include
-I/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include
-I/usr/local/include -I/usr/include -I.
-I/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include
-Isrc -Iagg24/include -I. -I/usr/include/python2.6 -c
CXX/IndirectPythonInterface.cxx -o
build/temp.linux-x86_64-2.6/CXX/IndirectPythonInterface.o

gcc -pthread -fno-strict-aliasing -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2
-fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic
-D_GNU_SOURCE -fPIC -fwrapv -DNDEBUG -O2 -g -pipe -Wall
-Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector
--param=ssp-buffer-size=4 -m64 -mtune=generic -D_GNU_SOURCE -fPIC -fwrapv
-fPIC -DPY_ARRAY_UNIQUE_SYMBOL=MPL_ARRAY_API -DPYCXX_ISO_CPP_LIB=1
-I/usr/local/include -I/usr/include
-I/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include
-I/usr/local/include -I/usr/include -I.
-I/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include
-Isrc -Iagg24/include -I. -I/usr/include/python2.6 -c CXX/cxxextensions.c -o
build/temp.linux-x86_64-2.6/CXX/cxxextensions.o

g++ -pthread -shared build/temp.linux-x86_64-2.6/src/image.o
build/temp.linux-x86_64-2.6/src/mplutils.o
build/temp.linux-x86_64-2.6/agg24/src/agg_trans_affine.o
build/temp.linux-x86_64-2.6/agg24/src/agg_image_filters.o
build/temp.linux-x86_64-2.6/agg24/src/agg_bezier_arc.o
build/temp.linux-x86_64-2.6/CXX/cxxsupport.o
build/temp.linux-x86_64-2.6/CXX/cxx_extensions.o
build/temp.linux-x86_64-2.6/CXX/IndirectPythonInterface.o
build/temp.linux-x86_64-2.6/CXX/cxxextensions.o -L/usr/local/lib -L/usr/lib
-L/usr/local/lib64 -L/usr/lib64 -L/usr/lib64 -lstdc++ -lm -lpython2.6 -o
build/lib.linux-x86_64-2.6/matplotlib/_image.so

building 'matplotlib._png' extension

gcc -pthread -fno-strict-aliasing -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2
-fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic
-D_GNU_SOURCE -fPIC -fwrapv -DNDEBUG -O2 -g -pipe -Wall
-Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector
--param=ssp-buffer-size=4 -m64 -mtune=generic -D_GNU_SOURCE -fPIC -fwrapv
-fPIC -DPY_ARRAY_UNIQUE_SYMBOL=MPL_ARRAY_API -DPYCXX_ISO_CPP_LIB=1
-I/usr/local/include -I/usr/include -I/usr/local/include -I/usr/include -I.
-I/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include
-I. -I/usr/include/python2.6 -c src/_png.cpp -o
build/temp.linux-x86_64-2.6/src/_png.o

src/_png.cpp:10:20: error: png.h: No such file or directory

In file included from
/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/ndarraytypes.h:1728,

                 from
/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/ndarrayobject.h:17,

                 from
/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/arrayobject.h:15,

                 from src/_png.cpp:28:

/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/npy_deprecated_api.h:11:2:
warning: #warning "Using deprecated NumPy API, disable it by #defining
NPY_NO_DEPRECATED_API NPY_1_7_API_VERSION"

In file included from src/file_compat.h:4,

                 from src/_png.cpp:30:

/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/npy_3kcompat.h:
In function ‘PyObject* npy_PyFile_OpenFile(PyObject*, const char*)’:

/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/npy_3kcompat.h:247:
warning: deprecated conversion from string constant to ‘char*’

/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/npy_3kcompat.h:
In function ‘int npy_PyFile_CloseFile(PyObject*)’:

/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/npy_3kcompat.h:255:
warning: deprecated conversion from string constant to ‘char*’

src/_png.cpp: At global scope:

src/_png.cpp:67: error: variable or field ‘write_png_data’ declared void

src/_png.cpp:67: error: ‘png_structp’ was not declared in this scope

src/_png.cpp:67: error: ‘png_bytep’ was not declared in this scope

src/_png.cpp:67: error: ‘png_size_t’ was not declared in this scope

/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/__multiarray_api.h:1594:
warning: ‘int _import_array()’ defined but not used

error: command 'gcc' failed with exit status 1

----------------------------------------
Command /home/webalert/.virtualenvs/mandala/bin/python -c "import
setuptools;__file__='/home/webalert/.virtualenvs/mandala/build/matplotlib/setup.py';exec(compile(open(__file__).read().replace('\r\n',
'\n'), __file__, 'exec'))" install --record
/tmp/pip-5AdrTx-record/install-record.txt
--single-version-externally-managed --install-headers
/home/webalert/.virtualenvs/mandala/include/site/python2.6 failed with error
code 1 in /home/webalert/.virtualenvs/mandala/build/matplotlib
Storing complete log in /home/webalert/.pip/pip.log
(mandala)[webalert@localhost ~]$ sudo yum-builddep python-matplotlib
[sudo] password for webalert: 
Loaded plugins: fastestmirror, refresh-packagekit
Loading mirror speeds from cached hostfile
 * base: centos.mirror.ca.planethoster.net
 * extras: mirror.science.uottawa.ca
 * rpmforge: mirror.team-cymru.org
 * updates: centos.mirror.ca.planethoster.net
Checking for new repos for mirrors
No source RPM found for python-matplotlib-0.99.1.2-1.el6.x86_64
No uninstalled build requires
(mandala)[webalert@localhost ~]$ pip install matplotlib
Downloading/unpacking matplotlib
  Running setup.py egg_info for package matplotlib
    basedirlist is: ['/usr/local', '/usr']
   
============================================================================
    BUILDING MATPLOTLIB
                matplotlib: 1.2.1
                    python: 2.6.6 (r266:84292, Feb 22 2013, 00:00:18)  [GCC
                            4.4.7 20120313 (Red Hat 4.4.7-3)]
                  platform: linux2
    
    REQUIRED DEPENDENCIES
                     numpy: 1.7.1
                 freetype2: 9.22.3
    
    OPTIONAL BACKEND DEPENDENCIES
                    libpng: found, but unknown version (no pkg-config)
                            * Could not find 'libpng' headers in any of
                            * '/usr/local/include', '/usr/include',
                            * '/usr/local/include', '/usr/include', '.'
                   Tkinter: no
                            * TKAgg requires Tkinter
                      Gtk+: no
                            * Building for Gtk+ requires pygtk; you must be
able
                            * to "import gtk" in your build/install
environment
           Mac OS X native: no
                        Qt: no
                       Qt4: no
                    PySide: no
                     Cairo: no
    
    OPTIONAL DATE/TIMEZONE DEPENDENCIES
                  dateutil: matplotlib will provide
                      pytz: matplotlib will provide
    
    OPTIONAL USETEX DEPENDENCIES
                    dvipng: no
               ghostscript: 8.70
                     latex: no
                   pdftops: 0.12.4
    
    [Edit setup.cfg to suppress the above messages]
   
============================================================================
    pymods ['pylab']
    packages ['matplotlib', 'matplotlib.backends',
'matplotlib.backends.qt4_editor', 'matplotlib.projections',
'matplotlib.testing', 'matplotlib.testing.jpl_units', 'matplotlib.tests',
'mpl_toolkits', 'mpl_toolkits.mplot3d', 'mpl_toolkits.axes_grid',
'mpl_toolkits.axes_grid1', 'mpl_toolkits.axisartist',
'matplotlib.sphinxext', 'matplotlib.tri', 'matplotlib.delaunay', 'pytz',
'dateutil', 'dateutil.zoneinfo']
    warning: no files found matching 'KNOWN_BUGS'
    warning: no files found matching 'INTERACTIVE'
    warning: no files found matching 'make.osx'
    warning: no files found matching 'MANIFEST'
    warning: no files found matching '__init__.py'
    warning: no files found matching 'examples/data/*'
    warning: no files found matching 'lib/mpl_toolkits'
    warning: no files found matching
'lib/matplotlib/mpl-data/matplotlib.conf'
    warning: no files found matching
'lib/matplotlib/mpl-data/matplotlib.conf.template'
    warning: manifest_maker: MANIFEST.in, line 16: 'recursive-include'
expects <dir> <pattern1> <pattern2> ...
    warning: no files found matching 'LICENSE*' under directory 'license'
Installing collected packages: matplotlib
  Running setup.py install for matplotlib
    basedirlist is: ['/usr/local', '/usr']
   
============================================================================
    BUILDING MATPLOTLIB
                matplotlib: 1.2.1
                    python: 2.6.6 (r266:84292, Feb 22 2013, 00:00:18)  [GCC
                            4.4.7 20120313 (Red Hat 4.4.7-3)]
                  platform: linux2
    
    REQUIRED DEPENDENCIES
                     numpy: 1.7.1
                 freetype2: 9.22.3
    
    OPTIONAL BACKEND DEPENDENCIES
                    libpng: found, but unknown version (no pkg-config)
                            * Could not find 'libpng' headers in any of
                            * '/usr/local/include', '/usr/include',
                            * '/usr/local/include', '/usr/include', '.'
                   Tkinter: no
                            * TKAgg requires Tkinter
                      Gtk+: no
                            * Building for Gtk+ requires pygtk; you must be
able
                            * to "import gtk" in your build/install
environment
           Mac OS X native: no
                        Qt: no
                       Qt4: no
                    PySide: no
                     Cairo: no
    
    OPTIONAL DATE/TIMEZONE DEPENDENCIES
                  dateutil: matplotlib will provide
                      pytz: matplotlib will provide
    
    OPTIONAL USETEX DEPENDENCIES
                    dvipng: no
               ghostscript: 8.70
                     latex: no
                   pdftops: 0.12.4
    
    [Edit setup.cfg to suppress the above messages]
   
============================================================================
    pymods ['pylab']
    packages ['matplotlib', 'matplotlib.backends',
'matplotlib.backends.qt4_editor', 'matplotlib.projections',
'matplotlib.testing', 'matplotlib.testing.jpl_units', 'matplotlib.tests',
'mpl_toolkits', 'mpl_toolkits.mplot3d', 'mpl_toolkits.axes_grid',
'mpl_toolkits.axes_grid1', 'mpl_toolkits.axisartist',
'matplotlib.sphinxext', 'matplotlib.tri', 'matplotlib.delaunay', 'pytz',
'dateutil', 'dateutil.zoneinfo']
    building 'matplotlib._png' extension
    gcc -pthread -fno-strict-aliasing -O2 -g -pipe -Wall
-Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector
--param=ssp-buffer-size=4 -m64 -mtune=generic -D_GNU_SOURCE -fPIC -fwrapv
-DNDEBUG -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions
-fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic
-D_GNU_SOURCE -fPIC -fwrapv -fPIC -DPY_ARRAY_UNIQUE_SYMBOL=MPL_ARRAY_API
-DPYCXX_ISO_CPP_LIB=1 -I/usr/local/include -I/usr/include
-I/usr/local/include -I/usr/include -I.
-I/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include
-I. -I/usr/include/python2.6 -c src/_png.cpp -o
build/temp.linux-x86_64-2.6/src/_png.o
    src/_png.cpp:10:20: error: png.h: No such file or directory
    In file included from
/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/ndarraytypes.h:1728,
                     from
/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/ndarrayobject.h:17,
                     from
/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/arrayobject.h:15,
                     from src/_png.cpp:28:
   
/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/npy_deprecated_api.h:11:2:
warning: #warning "Using deprecated NumPy API, disable it by #defining
NPY_NO_DEPRECATED_API NPY_1_7_API_VERSION"
    In file included from src/file_compat.h:4,
                     from src/_png.cpp:30:
   
/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/npy_3kcompat.h:
In function ‘PyObject* npy_PyFile_OpenFile(PyObject*, const char*)’:
   
/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/npy_3kcompat.h:247:
warning: deprecated conversion from string constant to ‘char*’
   
/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/npy_3kcompat.h:
In function ‘int npy_PyFile_CloseFile(PyObject*)’:
   
/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/npy_3kcompat.h:255:
warning: deprecated conversion from string constant to ‘char*’
    src/_png.cpp: At global scope:
    src/_png.cpp:67: error: variable or field ‘write_png_data’ declared void
    src/_png.cpp:67: error: ‘png_structp’ was not declared in this scope
    src/_png.cpp:67: error: ‘png_bytep’ was not declared in this scope
    src/_png.cpp:67: error: ‘png_size_t’ was not declared in this scope
   
/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/__multiarray_api.h:1594:
warning: ‘int _import_array()’ defined but not used
    error: command 'gcc' failed with exit status 1
    Complete output from command
/home/webalert/.virtualenvs/mandala/bin/python -c "import
setuptools;__file__='/home/webalert/.virtualenvs/mandala/build/matplotlib/setup.py';exec(compile(open(__file__).read().replace('\r\n',
'\n'), __file__, 'exec'))" install --record
/tmp/pip-9i4ni6-record/install-record.txt
--single-version-externally-managed --install-headers
/home/webalert/.virtualenvs/mandala/include/site/python2.6:
    basedirlist is: ['/usr/local', '/usr']

============================================================================

BUILDING MATPLOTLIB

            matplotlib: 1.2.1

                python: 2.6.6 (r266:84292, Feb 22 2013, 00:00:18)  [GCC

                        4.4.7 20120313 (Red Hat 4.4.7-3)]

              platform: linux2



REQUIRED DEPENDENCIES

                 numpy: 1.7.1

             freetype2: 9.22.3



OPTIONAL BACKEND DEPENDENCIES

                libpng: found, but unknown version (no pkg-config)

                        * Could not find 'libpng' headers in any of

                        * '/usr/local/include', '/usr/include',

                        * '/usr/local/include', '/usr/include', '.'

               Tkinter: no

                        * TKAgg requires Tkinter

                  Gtk+: no

                        * Building for Gtk+ requires pygtk; you must be able

                        * to "import gtk" in your build/install environment

       Mac OS X native: no

                    Qt: no

                   Qt4: no

                PySide: no

                 Cairo: no



OPTIONAL DATE/TIMEZONE DEPENDENCIES

              dateutil: matplotlib will provide

                  pytz: matplotlib will provide



OPTIONAL USETEX DEPENDENCIES

                dvipng: no

           ghostscript: 8.70

                 latex: no

               pdftops: 0.12.4



[Edit setup.cfg to suppress the above messages]

============================================================================

pymods ['pylab']

packages ['matplotlib', 'matplotlib.backends',
'matplotlib.backends.qt4_editor', 'matplotlib.projections',
'matplotlib.testing', 'matplotlib.testing.jpl_units', 'matplotlib.tests',
'mpl_toolkits', 'mpl_toolkits.mplot3d', 'mpl_toolkits.axes_grid',
'mpl_toolkits.axes_grid1', 'mpl_toolkits.axisartist',
'matplotlib.sphinxext', 'matplotlib.tri', 'matplotlib.delaunay', 'pytz',
'dateutil', 'dateutil.zoneinfo']

running install

running build

running build_py

copying lib/matplotlib/mpl-data/matplotlibrc ->
build/lib.linux-x86_64-2.6/matplotlib/mpl-data

running build_ext

building 'matplotlib._png' extension

gcc -pthread -fno-strict-aliasing -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2
-fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic
-D_GNU_SOURCE -fPIC -fwrapv -DNDEBUG -O2 -g -pipe -Wall
-Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector
--param=ssp-buffer-size=4 -m64 -mtune=generic -D_GNU_SOURCE -fPIC -fwrapv
-fPIC -DPY_ARRAY_UNIQUE_SYMBOL=MPL_ARRAY_API -DPYCXX_ISO_CPP_LIB=1
-I/usr/local/include -I/usr/include -I/usr/local/include -I/usr/include -I.
-I/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include
-I. -I/usr/include/python2.6 -c src/_png.cpp -o
build/temp.linux-x86_64-2.6/src/_png.o

src/_png.cpp:10:20: error: png.h: No such file or directory

In file included from
/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/ndarraytypes.h:1728,

                 from
/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/ndarrayobject.h:17,

                 from
/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/arrayobject.h:15,

                 from src/_png.cpp:28:

/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/npy_deprecated_api.h:11:2:
warning: #warning "Using deprecated NumPy API, disable it by #defining
NPY_NO_DEPRECATED_API NPY_1_7_API_VERSION"

In file included from src/file_compat.h:4,

                 from src/_png.cpp:30:

/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/npy_3kcompat.h:
In function ‘PyObject* npy_PyFile_OpenFile(PyObject*, const char*)’:

/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/npy_3kcompat.h:247:
warning: deprecated conversion from string constant to ‘char*’

/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/npy_3kcompat.h:
In function ‘int npy_PyFile_CloseFile(PyObject*)’:

/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/npy_3kcompat.h:255:
warning: deprecated conversion from string constant to ‘char*’

src/_png.cpp: At global scope:

src/_png.cpp:67: error: variable or field ‘write_png_data’ declared void

src/_png.cpp:67: error: ‘png_structp’ was not declared in this scope

src/_png.cpp:67: error: ‘png_bytep’ was not declared in this scope

src/_png.cpp:67: error: ‘png_size_t’ was not declared in this scope

/home/webalert/.virtualenvs/mandala/lib/python2.6/site-packages/numpy/core/include/numpy/__multiarray_api.h:1594:
warning: ‘int _import_array()’ defined but not used

error: command 'gcc' failed with exit status 1

----------------------------------------
Command /home/webalert/.virtualenvs/mandala/bin/python -c "import
setuptools;__file__='/home/webalert/.virtualenvs/mandala/build/matplotlib/setup.py';exec(compile(open(__file__).read().replace('\r\n',
'\n'), __file__, 'exec'))" install --record
/tmp/pip-9i4ni6-record/install-record.txt
--single-version-externally-managed --install-headers
/home/webalert/.virtualenvs/mandala/include/site/python2.6 failed with error
code 1 in /home/webalert/.virtualenvs/mandala/build/matplotlib
Storing complete log in /home/webalert/.pip/pip.log
(mandala)[webalert@localhost ~]$ 


Could it be libpng?




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