Q:

/usr/local/include/tk.h:71:13: fatal error: 'X11/Xlib.h' file not found when install python library

I have a virtual env for python, and trying to install some packages in the virtual-env:
sudo /Users/edamame/Library/python_virenv/bin/pip install matplotlib

Then I got the following error:
  :
  :
clang: warning: -framework Tcl: 'linker' input unused

clang: warning: -framework Tk: 'linker' input unused

In file included from src/_tkagg.cpp:28:

/usr/local/include/tk.h:71:13: fatal error: 'X11/Xlib.h' file not found

#   include <X11/Xlib.h>

            ^

1 error generated.

error: command 'cc' failed with exit status 1

I am on Mac El-Captain, and I have:
edamame$ locate Xlib.h
WARNING: The locate database (/var/db/locate.database) does not exist.
To create the database, run the following command:

  sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.locate.plist

Please be aware that the database can take some time to generate; once
the database has been created, this message will no longer appear.

Any idea how I can fix this problem? Thanks!

A:

You should either install the development files for X11 (from memory: libx11-dev), or if they are already installed, add the X11 directory to your include search path. 
You can use locate Xlib.h to figure out if the files are already there. Use the -I compiler option to add directories to your search path.

