我在控制台中写道：
pip3 install matplotlib
以及由此产生的错误：
Collecting matplotlib
Using cached https://files.pythonhosted.org/packages/89/0c/653aec68e9cfb775c4fbae8f71011206e5e7fe4d60fcf01ea1a9d3bc957f/matplotlib-3.0.2.tar.gz
Complete output from command python setup.py egg_info:
============================================================================
Edit setup.cfg to change the build options
BUILDING MATPLOTLIB
matplotlib: yes [3.0.2]
python: yes [3.5.2 (default, Sep 14 2017, 22:51:06) [GCC
5.4.0 20160609]]
platform: yes [linux]
REQUIRED DEPENDENCIES AND EXTENSIONS
numpy: yes [version 1.15.4]
install_requires: yes [handled by setuptools]
libagg: yes [pkg-config information for 'libagg' could not
be found. Using local copy.]
freetype: no [The C/C++ header for freetype2 (ft2build.h)
could not be found. You may need to install the
development package.]
png: no [pkg-config information for 'libpng' could not
be found.]
qhull: yes [pkg-config information for 'libqhull' could not
be found. Using local copy.]
OPTIONAL SUBPACKAGES
sample_data: yes [installing]
toolkits: yes [installing]
tests: no [skipping due to configuration]
toolkits_tests: no [skipping due to configuration]
OPTIONAL BACKEND EXTENSIONS
agg: yes [installing]
tkagg: yes [installing; run-time loading from Python Tcl /
Tk]
macosx: no [Mac OS-X only]
windowing: no [Microsoft Windows only]
OPTIONAL PACKAGE DATA
dlls: no [skipping due to configuration]
============================================================================
* The following required packages can not be built:
* freetype, png
----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /tmp/pip-install-izaasteb/matplotlib/
操作系统：linux mint
解决方案原来是：