Develop Reference

Pyenv broke after upgrading to Big Sur

Pyenv has not worked since upgrading to Big Sur. This is how it started:
❯ pyenv install 3.8.0
python-build: use openssl#1.1 from homebrew
python-build: use readline from homebrew
Downloading Python-3.8.0.tar.xz...
-> https://www.python.org/ftp/python/3.8.0/Python-3.8.0.tar.xz
Installing Python-3.8.0...
python-build: use readline from homebrew
BUILD FAILED (OS X 11.1 using python-build 20180424)
Inspect or clean up the working tree at /var/folders/_y/vdsjczjj3nvflspjcl8r68zr0000gq/T/python-build.20210131003659.3456
Results logged to /var/folders/_y/vdsjczjj3nvflspjcl8r68zr0000gq/T/python-build.20210131003659.3456.log
Last 10 log lines:
checking for python3.8... python3.8
checking for --enable-universalsdk... no
checking for --with-universal-archs... no
checking MACHDEP... "darwin"
checking for gcc... clang
checking whether the C compiler works... no
configure: error: in `/var/folders/_y/vdsjczjj3nvflspjcl8r68zr0000gq/T/python-build.20210131003659.3456/Python-3.8.0':
configure: error: C compiler cannot create executables
See `config.log' for more details
xcrun: error: invalid active developer path (/Library/Developer/CommandLineTools), missing xcrun at: /Library/Developer/CommandLineTools/usr/bin/xcrun
So I ran xcode-select --install. It went through, though I don't see a xrun directory under /Library/Developer/CommandLineTools/usr/bin/.
I read many different github issues' pages, StackOverflow posts, and tried many different things including brew install zlib sqlite bzip2 libiconv libzip. This is where I am right now:
❯ pyenv install 3.8.0
python-build: use openssl#1.1 from homebrew
python-build: use readline from homebrew
Downloading Python-3.8.0.tar.xz...
-> https://www.python.org/ftp/python/3.8.0/Python-3.8.0.tar.xz
Installing Python-3.8.0...
python-build: use readline from homebrew
python-build: use zlib from xcode sdk
BUILD FAILED (OS X 11.1 using python-build 20180424)
Inspect or clean up the working tree at /var/folders/_y/vdsjczjj3nvflspjcl8r68zr0000gq/T/python-build.20210201012936.8553
Results logged to /var/folders/_y/vdsjczjj3nvflspjcl8r68zr0000gq/T/python-build.20210201012936.8553.log
Last 10 log lines:
^
clang -fno-strict-aliasing -Wsign-compare -Wunreachable-code -DNDEBUG -g -fwrapv -O3 -Wall -I/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include -L /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include -L brew --prefix bzip2/include -I/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include -L /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include -L brew --prefix bzip2/include -std=c99 -Werror=implicit-function-declaration -I./Include/internal -I. -I./Include -I/usr/local/opt/readline/include -I/usr/local/opt/readline/include -I/Users/rayhanmuktader/.pyenv/versions/3.8.0/include -I/usr/local/opt/readline/include -I/usr/local/opt/readline/include -I/Users/rayhanmuktader/.pyenv/versions/3.8.0/include -DPy_BUILD_CORE_BUILTIN -c ./Modules/pwdmodule.c -o Modules/pwdmodule.o
clang: warning: argument unused during compilation: '-L/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include' [-Wunused-command-line-argument]
clang: warning: argument unused during compilation: '-Lbrew' [-Wunused-command-line-argument]
c
lang: warning: argument unused during compilation: '-L/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include' [-Wunused-command-line-argument]
clang: warning: argument unused during compilation: '-Lbrew' [-Wunused-command-line-argument]
1 error generated.
make: *** [Modules/posixmodule.o] Error 1
make: *** Waiting for unfinished jobs....
1 warning generated.
My .zshrc looks this at the moment:
if command -v pyenv 1>/dev/null 2>&1; then
eval "$(pyenv init -)"
fi
export PATH="$HOME/.poetry/bin:$PATH"
export LDFLAGS="-L $(xcrun --show-sdk-path)/usr/lib -L brew --prefix bzip2/lib"
export CFLAGS="-L $(xcrun --show-sdk-path)/usr/include -L brew --prefix bzip2/include"
I also tried SYSTEM_VERSION_COMPAT=1 pyenv install 3.8.0 but that didn't solve it either. If it helps anything, note that it hangs for an unusually long time at python-build: use zlib from xcode sdk line.
Thank you if read this far. Any help would be greatly appreciated.

This is what worked for me (kind of).
I followed step 1 and step 2 from https://koji-kanao.medium.com/install-python-3-8-0-via-pyenv-on-bigsur-b4246987a548
I upgraded to BigSur 11.2, installed XCode 12.5 beta from https://developer.apple.com/xcode/resources/. I also installed Command Line Tools for Xcode 12.5 beta from https://developer.apple.com/download/more/?=command%20line%20tools (I don't know if this was necessary)
My .zshrc looks like this:
eval "$(pyenv init -)"
fi
export PATH="$HOME/.poetry/bin:$PATH"
Then in order to install python 3.8.0 I ran:
$ CFLAGS="-I$(brew --prefix openssl)/include -I$(brew --prefix bzip2)/include -I$(brew --prefix readline)/include -I$(xcrun --show-sdk-path)/usr/include" LDFLAGS="-L$(brew --prefix openssl)/lib -L$(brew --prefix readline)/lib -L$(brew --prefix zlib)/lib -L$(brew --prefix bzip2)/lib" pyenv install --patch 3.8.0 < <(curl -sSL https://github.com/python/cpython/commit/8ea6353.patch\?full_index\=1)
This actually installed it. HOWEVER, when I ran poetry install on an existing project, it started installing the package then it suddenly blew up with the following error:
• Installing pynacl (1.3.0): Failed
ERROR: Failed building wheel for PyNaCl
Failed to build PyNaCl
ERROR: Could not build wheels for PyNaCl which use PEP 517 and cannot be installed directly
WARNING: You are using pip version 20.2.2; however, version 21.0.1 is available.
You should consider upgrading via the '/Users/rayhanmuktader/Library/Caches/pypoetry/virtualenvs/desk-backend-kAA1Wc9W-py3.8/bin/python -m pip install --upgrade pip' command.
at ~/.poetry/lib/poetry/utils/env.py:1074 in _run
1070│ output = subprocess.check_output(
1071│ cmd, stderr=subprocess.STDOUT, **kwargs
1072│ )
1073│ except CalledProcessError as e:
→ 1074│ raise EnvCommandError(e, input=input_)
1075│
1076│ return decode(output)
1077│
1078│ def execute(self, bin, *args, **kwargs):
The solution to this problem was running $ /Users/rayhanmuktader/Library/Caches/pypoetry/virtualenvs/desk-backend-kAA1Wc9W-py3.8/bin/python -m pip install pynacl==1.3.0 to install the pynacl package. Then running poetry install again to continue the installation process. Rinse and repeat for every package it fails to install through poetry install.

Installing python-igraph with pip on Mac 10.14 fails with "library not found for -lstdc++"

I am trying to install python-igraph using pip3 on Mac OS X 10.14, but the installation fails with the following error message:
$ pip3 install python-igraph
...snip...
gcc -bundle -undefined dynamic_lookup -L/Users/charles/.pyenv/versions/miniconda3-4.3.30/lib -arch x86_64 -L/Users/charles/.pyenv/versions/miniconda3-4.3.30/lib -arch x86_64 -arch x86_64 build/temp.macosx-10.7-x86_64-3.6/src/edgeobject.o build/temp.macosx-10.7-x86_64-3.6/src/common.o build/temp.macosx-10.7-x86_64-3.6/src/py2compat.o build/temp.macosx-10.7-x86_64-3.6/src/graphobject.o build/temp.macosx-10.7-x86_64-3.6/src/indexing.o build/temp.macosx-10.7-x86_64-3.6/src/igraphmodule.o build/temp.macosx-10.7-x86_64-3.6/src/bfsiter.o build/temp.macosx-10.7-x86_64-3.6/src/convert.o build/temp.macosx-10.7-x86_64-3.6/src/vertexobject.o build/temp.macosx-10.7-x86_64-3.6/src/random.o build/temp.macosx-10.7-x86_64-3.6/src/edgeseqobject.o build/temp.macosx-10.7-x86_64-3.6/src/error.o build/temp.macosx-10.7-x86_64-3.6/src/vertexseqobject.o build/temp.macosx-10.7-x86_64-3.6/src/arpackobject.o build/temp.macosx-10.7-x86_64-3.6/src/attributes.o build/temp.macosx-10.7-x86_64-3.6/src/filehandle.o build/temp.macosx-10.7-x86_64-3.6/src/pyhelpers.o igraphcore/lib/libigraph.a -Ligraphcore/lib -L/usr/local/lib -L/usr/lib -lxml2 -lz -lm -lstdc++ -o build/lib.macosx-10.7-x86_64-3.6/igraph/_igraph.cpython-36m-darwin.so
clang: warning: libstdc++ is deprecated; move to libc++ with a minimum deployment target of OS X 10.9 [-Wdeprecated]
ld: library not found for -lstdc++
clang: error: linker command failed with exit code 1 (use -v to see invocation)
error: command 'gcc' failed with exit status 1
gcc version:
$ gcc --version
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk/usr/include/c++/4.2.1
Apple LLVM version 10.0.1 (clang-1001.0.46.4)
Target: x86_64-apple-darwin18.7.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
python version:
$ python3 --version
Python 3.6.7
(Side note, python and python3 point to the same python, and pip and pip3 point to the same (corresponding) pip.)
I also tried running xcode-select --install but this told me 'command line tools are already installed, use "Software Update" to install updates' (Xcode is up to date).

Run
export MACOSX_DEPLOYMENT_TARGET=10.9
before running pip install python-igraph. Then you should see it install successfully:
$ pip install python-igraph
Collecting python-igraph
Using cached https://files.pythonhosted.org/packages/0f/a0/4e7134f803737aa6eebb4e5250565ace0e2599659e22be7f7eba520ff017/python-igraph-0.7.1.post6.tar.gz
Building wheels for collected packages: python-igraph
Running setup.py bdist_wheel for python-igraph ... done
Stored in directory: /Users/charles/Library/Caches/pip/wheels/41/d6/02/34eebae97e25f5b87d60f4c0687e00523e3f244fa41bc3f4a7
Successfully built python-igraph
Installing collected packages: python-igraph
Successfully installed python-igraph-0.7.1.post6

python install PIL on windows [duplicate]

I am trying to install PIL (the Python Imaging Library) using the command:
sudo pip install pil
but I get the following message:
Downloading/unpacking PIL
You are installing a potentially insecure and unverifiable file. Future versions of pip will default to disallowing insecure files.
Downloading PIL-1.1.7.tar.gz (506kB): 506kB downloaded
Running setup.py egg_info for package PIL
WARNING: '' not a valid package name; please use only.-separated package names in setup.py
Installing collected packages: PIL
Running setup.py install for PIL
WARNING: '' not a valid package name; please use only.-separated package names in setup.py
--- using frameworks at /System/Library/Frameworks
building '_imaging' extension
clang -fno-strict-aliasing -fno-common -dynamic -g -Os -pipe -fno-common -fno-strict-aliasing -fwrapv -mno-fused-madd -DENABLE_DTRACE -DMACOSX -DNDEBUG -Wall -Wstrict-prototypes -Wshorten-64-to-32 -DNDEBUG -g -Os -Wall -Wstrict-prototypes -DENABLE_DTRACE -arch i386 -arch x86_64 -pipe -IlibImaging -I/System/Library/Frameworks/Python.framework/Versions/2.7/include -I/System/Library/Frameworks/Python.framework/Versions/2.7/include/python2.7 -c _imaging.c -o build/temp.macosx-10.8-intel-2.7/_imaging.o
unable to execute clang: No such file or directory
error: command 'clang' failed with exit status 1
Complete output from command /usr/bin/python -c "import setuptools;__file__='/private/tmp/pip_build_root/PIL/setup.py';exec(compile(open(__file__).read().replace('\r\n', '\n'), __file__, 'exec'))" install --record /tmp/pip-AYrxVD-record/install-record.txt --single-version-externally-managed:
WARNING: '' not a valid package name; please use only.-separated package names in setup.py
running install
running build
.
.
.
.
copying PIL/XVThumbImagePlugin.py -> build/lib.macosx-10.8-intel-2.7
running build_ext
--- using frameworks at /System/Library/Frameworks
building '_imaging' extension
creating build/temp.macosx-10.8-intel-2.7
creating build/temp.macosx-10.8-intel-2.7/libImaging
clang -fno-strict-aliasing -fno-common -dynamic -g -Os -pipe -fno-common -fno-strict-aliasing -fwrapv -mno-fused-madd -DENABLE_DTRACE -DMACOSX -DNDEBUG -Wall -Wstrict-prototypes -Wshorten-64-to-32 -DNDEBUG -g -Os -Wall -Wstrict-prototypes -DENABLE_DTRACE -arch i386 -arch x86_64 -pipe -IlibImaging -I/System/Library/Frameworks/Python.framework/Versions/2.7/include -I/System/Library/Frameworks/Python.framework/Versions/2.7/include/python2.7 -c _imaging.c -o build/temp.macosx-10.8-intel-2.7/_imaging.o
unable to execute clang: No such file or directory
error: command 'clang' failed with exit status 1
----------------------------------------
Cleaning up…
Could you please help me to install PIL?

Install Xcode and Xcode Command Line Tools as mentioned.
Use Pillow instead, as PIL is basically dead. Pillow is a maintained fork of PIL.
https://pypi.org/project/Pillow/
pip install Pillow
If you have both Pythons installed and want to install this for Python3:
python3 -m pip install Pillow

This works for me:
apt-get install python-dev
apt-get install libjpeg-dev
apt-get install libjpeg8-dev
apt-get install libpng3
apt-get install libfreetype6-dev
ln -s /usr/lib/i386-linux-gnu/libfreetype.so /usr/lib
ln -s /usr/lib/i386-linux-gnu/libjpeg.so /usr/lib
ln -s /usr/lib/i386-linux-gnu/libz.so /usr/lib
pip install PIL --allow-unverified PIL --allow-all-external

It is very simple using apt install use this command to get it done
sudo apt-get install python-PIL
or
sudo pip install pillow
or
sudo easy_install pillow

Install
pip install Pillow
Then, Just import in your file like,
from PIL import Image
I am using windows. It is working for me.
NOTE:
Pillow is a functional drop-in replacement for the Python Imaging
Library. To run your existing PIL-compatible code with Pillow, it
needs to be modified to import the Imaging module from the PIL
namespace instead of the global namespace.
i.e. change:
import Image
to:
from PIL import Image
https://pypi.org/project/Pillow/2.2.1/

You should install as described here:
pip install image

On Mac OS X, use this command:
sudo pip install https://effbot.org/media/downloads/Imaging-1.1.7.tar.gz

I got the answer from a discussion here:
I tried
pip install --no-index -f http://dist.plone.org/thirdparty/ -U PIL
and it worked.

I take it you're on Mac. See How can I install PIL on mac os x 10.7.2 Lion
If you use homebrew, you can install the PIL with just brew install pil. You may then need to add the install directory ($(brew --prefix)/lib/python2.7/site-packages) to your PYTHONPATH, or add the location of PIL directory itself in a file called PIL.pth file in
any of your site-packages directories, with the contents:
/usr/local/lib/python2.7/site-packages/PIL
(assuming brew --prefix is /usr/local).
Alternatively, you can just download/build/install it from source:
# download
curl -O -L http://effbot.org/media/downloads/Imaging-1.1.7.tar.gz
# extract
tar -xzf Imaging-1.1.7.tar.gz
cd Imaging-1.1.7
# build and install
python setup.py build
sudo python setup.py install
# or install it for just you without requiring admin permissions:
# python setup.py install --user
I ran the above just now (on OSX 10.7.2, with XCode 4.2.1 and System
Python 2.7.1) and it built just fine, though there is a possibility
that something in my environment is non-default.

These days, everyone uses Pillow, a friendly PIL fork, over PIL.
Instead of: sudo pip install pil
Do: sudo pip install pillow
$ sudo apt-get install python-imaging
$ sudo -H pip install pillow

For Ubuntu, PIL is not working any more. I always get:
No matching distribution found for PIL
So install python-imaging:
sudo apt-get install python-imaging

I'm having the same problem, but it gets solved with installation of python-dev.
Before installing PIL, run following command:
sudo apt-get install python-dev
Then install PIL:
pip install PIL

I had some errors during installation. Just in case somebody has this too. Despite that I already was sitting under admin user, but not root.
File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/os.py", line 157, in makedirs
mkdir(name, mode)
OSError: [Errno 13] Permission denied: '/Library/Python/2.7/site-packages/PIL'
Storing debug log for failure in /Users/wzbozon/Library/Logs/pip.log
Adding "sudo" solved the problem, with sudo it worked:
~/Documents/mv-server: $ sudo pip install Pillow

For CentOS:
yum install python-imaging

I tried all the answers, but failed.
Directly get the source from the official site and then build install success.
Go to the site http://www.pythonware.com/products/pil/#pil117
Click "Python Imaging Library 1.1.7 Source Kit" to download the source
tar xf Imaging-1.1.7.tar.gz
cd Imaging-1.1.7
sudo python setup.py install

I nailed it by using sudo port install py27-Pillow

Try this:
sudo pip install PIL --allow-external PIL --allow-unverified PIL

(Window) If Pilow not work try download pil at http://www.pythonware.com/products/pil/

First you should run this sudo apt-get build-dep python-imaging which will give you all the dependencies that you might need
Then run sudo apt-get update && sudo apt-get -y upgrade
Followed by sudo apt-get install python-pip
And then finally install Pil pip install pillow

Search on package manager before using pip. On Arch linux you can get PIL by pacman -S python2-pillow

For Ubuntu, you can install PIL using apt install:
For Python 3 use:
sudo apt install python3-pil
For Python 2 use:
sudo apt install python-pil
Where pil should be lowercase as Clarkey252 points out

There's another Python package tool called conda. Conda is preferred (I believe) over pip when there are libraries that need to install C++ and other bindings that aren't pure Python. Conda includes pip in its installation as well so you can still use pip, but you also get the benefits of conda.
Conda also installs IPython, pil, and many other libraries by default. I think you'll like it.

Installing PyCrypto on Ubuntu - fatal error on build

Having looked at other similar threads, I still can't get pycrypto running.
I'm trying to get it working on my Ubuntu laptop - but I couldn't manage it on my Windows PC either.
I downloaded pycrypto-2.6, extracted it, and ran
python setup.py build
but then this happened
warning: GMP or MPIR library not found; Not building Crypto.PublicKey._fastmath.
building 'Crypto.Hash._MD2' extension
gcc -pthread -fno-strict-aliasing -fwrapv -Wall -Wstrict-prototypes -fPIC -std=c99 -O3 - fomit-frame-pointer -Isrc/ -I/usr/include/python2.7 -c src/MD2.c -o build/temp.linux-i686-?2.7/src/MD2.o
src/MD2.c:31:20: fatal error: Python.h: No such file or directory
compilation terminated.
error: command 'gcc' failed with exit status 1
Would appreciate any help.

You need to install the Python development files. I believe this will do it:
sudo apt-get install python-dev

On Ubuntu, I needed some other packages for it to succeed:
apt-get install autoconf g++ python2.7-dev
pip install pycrypto

On Ubuntu and if you use Python 3.x you will need:
sudo apt-get install gcc python3-dev
you probably already have gcc but just in case if you are trying this command from Dockerfile with base image python:3.6.4-slim-jessie then you will also need gcc.

August 2021
For python 3.8 users run
sudo apt-get install python3.8-dev
and try to install pycrypto again
pip install pycrypto

How can I install the Python library 'gevent' on Mac OS X Lion

Python library gevent, version 0.13.6 (the current version on PyPI) will not pip install on OS X Lion, Python 2.7 (and probably others.) It works fine on Snow Leopard.
How can I get this library installed?
Bonus points if it can be done using pip install, rather than a manual or custom process, because then it will play nicely with automated builds.
Here is my pip install output:
pip install gevent
Downloading/unpacking gevent
Running setup.py egg_info for package gevent
Requirement already satisfied (use --upgrade to upgrade): greenlet in ./tl_env/lib/python2.7/site-packages (from gevent)
Installing collected packages: gevent
Running setup.py install for gevent
building 'gevent.core' extension
gcc-4.2 -fno-strict-aliasing -fno-common -dynamic -isysroot /Developer/SDKs/MacOSX10.6.sdk -arch i386 -arch x86_64 -g -O2 -DNDEBUG -g -O3 -I/Library/Frameworks/Python.framework/Versions/2.7/include/python2.7 -c gevent/core.c -o build/temp.macosx-10.6-intel-2.7/gevent/core.o
In file included from gevent/core.c:225:
gevent/libevent.h:9:19: error: event.h: No such file or directory
gevent/libevent.h:38:20: error: evhttp.h: No such file or directory
gevent/libevent.h:39:19: error: evdns.h: No such file or directory
gevent/core.c:361: error: field ‘ev’ has incomplete type
gevent/core.c:741: warning: parameter names (without types) in function declaration
gevent/core.c: In function ‘__pyx_f_6gevent_4core___event_handler’:
gevent/core.c:1619: error: ‘EV_READ’ undeclared (first use in this function)
gevent/core.c:1619: error: (Each undeclared identifier is reported only once
gevent/core.c:15376: warning: assignment makes pointer from integer without a cast
[... about 1000 more lines of compiler errors...]
gevent/core.c:15385: error: dereferencing pointer to incomplete type
gevent/core.c: In function ‘__pyx_pf_6gevent_4core_4http___init__’:
gevent/core.c:15559: warning: assignment makes pointer from integer without a cast
gevent/core.c: At top level:
gevent/core.c:21272: error: expected ‘)’ before ‘val’
lipo: can't figure out the architecture type of: /var/folders/s5/t94kn0p10hdgxzx9_9sprpg40000gq/T//cczk54q7.out
error: command 'gcc-4.2' failed with exit status 1
Complete output from command /Users/jacob/code/toplevel/tl_env/bin/python -c "import setuptools;__file__='/Users/jacob/code/toplevel/tl_env/build/gevent/setup.py';exec(compile(open(__file__).read().replace('\r\n', '\n'), __file__, 'exec'))" install --single-version-externally-managed --record /var/folders/s5/t94kn0p10hdgxzx9_9sprpg40000gq/T/pip-s2hPd3-record/install-record.txt --install-headers /Users/jacob/code/toplevel/tl_env/bin/../include/site/python2.7:
running install
running build
running build_py
running build_ext
building 'gevent.core' extension
gcc-4.2 -fno-strict-aliasing -fno-common -dynamic -isysroot /Developer/SDKs/MacOSX10.6.sdk -arch i386 -arch x86_64 -g -O2 -DNDEBUG -g -O3 -I/Library/Frameworks/Python.framework/Versions/2.7/include/python2.7 -c gevent/core.c -o build/temp.macosx-10.6-intel-2.7/gevent/core.o

Don't post the entire thing! That's too much! 90% of the time, the first error is enough...
gevent/libevent.h:9:19: error: event.h: No such file or directory
This means that the library which provides the event.h header is not installed. The library is called libevent (website).
In general, compilation errors like these are a flaw in the build scripts. The build script should give an error message that libevent is not installed, and it is a bug that it did not do so.
To get libevent from MacPorts and then manually tell compiler with CFLAGS environment variable where to find event.h and libevent while running pip.
sudo port install libevent
CFLAGS="-I /opt/local/include -L /opt/local/lib" pip install gevent
You can also use homebrew for installing libevent : brew install libevent
(from David Wolever's comment)

CFLAGS='-std=c99' pip install gevent
See in: Can't install gevent OSX 10.11
on OS X 10.11, clang uses c11 as the default, so just turn it back to c99.

After a while, I realized that the paths for the CFLAGS variable mentioned above works when installing libevent from port, but not from brew. The following worked for me (on OSX Mavericks):
$ brew install libevent
$ export CFLAGS="-I /usr/local/Cellar/libevent/2.0.21/include -L /usr/local/Cellar/libevent/2.0.21/lib"
$ pip install gevent

This is the way I found the easiest:
install libevent using homebrew
$ brew install libevent
install gevent
$ pip install gevent
This was the only way I could get it to work.

Found this answer when looking for help installing on Snow Leopard, posting this in case someone else comes this way with the same problem.
I had libevent installed via macports.
export CFLAGS=-I/opt/local/include
export LDFLAGS=-L/opt/local/lib
sudo pip install gevent

I had libevent installed via brew and it failed too, what worked was similar to what Stephen done, but pointing to brew default install:
CFLAGS=-I/usr/local/include LDFLAGS=-L/usr/local/lib pip install gevent

In case you install all from sources and use csh the following works on mac os 10.9
download latest stable http://libevent.org/ libevent-2.0.21-stable
./configure
make
sudo make install
virtualenv env
source env/bin/activate.csh
setenv CFLAGS "-I /usr/local/include -L /usr/local/lib"
pip install gevent

I use virtualenv and virtualenv wrapper, and so I wanted this to be self contained. I got gevent working like so:
Assuming you have virtual env setup, then:
workon {my_virtual_env}
Then download libevent and install it against the virtualenv.
curl -L -O https://github.com/downloads/libevent/libevent/libevent-2.0.21-stable.tar.gz
tar -xzf libevent-2.0.21-stable.tar.gz
cd libevent-2.0.21-stable
./configure --prefix="$VIRTUAL_ENV"
make && make install
I'm assuming you've got gcc 5+ installed (I use brew)
Hope this helps.

sudo pip install cython git+git://github.com/gevent/gevent.git#egg=gevent

I am using MacOs High Sierra (10.13.3)
First I did :
brew install libevent
I upgraded my pip version to pip-18.0.
then tried installing again with following :-
pip install gevent
it worked.