title: ERROR: Failed building wheel for psycopg2
body: <p>I've been trying to connect my databse to pgadmin4. I connected it successfully but now my heroku app returns internal server error. In order to debug this I do <code>heroku logs -t</code> and it returns <code>ImportError: No module named psycopg2</code>. So I then try to do <code>pip install psycopg2</code> but I get the following error:</p>
  
  <pre><code>Collecting psycopg2
    Using cached psycopg2-2.8.5.tar.gz (380 kB)
  Building wheels for collected packages: psycopg2
    Building wheel for psycopg2 (setup.py) ... error
    ERROR: Command errored out with exit status 1:
     command: /Users/Documents/venv/bin/python -u -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/private/var/folders/yj/3jfym00d7r3_f9_jmkrt999r0000gn/T/pip-install-mpy9u7el/psycopg2/setup.py'"'"'; __file__='"'"'/private/var/folders/yj/3jfym00d7r3_f9_jmkrt999r0000gn/T/pip-install-mpy9u7el/psycopg2/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' bdist_wheel -d /private/var/folders/yj/3jfym00d7r3_f9_jmkrt999r0000gn/T/pip-wheel-z2s31ha_
         cwd: /private/var/folders/yj/3jfym00d7r3_f9_jmkrt999r0000gn/T/pip-install-mpy9u7el/psycopg2/
    Complete output (42 lines):
    running bdist_wheel
    running build
    running build_py
    creating build
    creating build/lib.macosx-10.15-x86_64-3.7
    creating build/lib.macosx-10.15-x86_64-3.7/psycopg2
    copying lib/_json.py -&gt; build/lib.macosx-10.15-x86_64-3.7/psycopg2
    copying lib/extras.py -&gt; build/lib.macosx-10.15-x86_64-3.7/psycopg2
    copying lib/compat.py -&gt; build/lib.macosx-10.15-x86_64-3.7/psycopg2
    copying lib/errorcodes.py -&gt; build/lib.macosx-10.15-x86_64-3.7/psycopg2
    copying lib/tz.py -&gt; build/lib.macosx-10.15-x86_64-3.7/psycopg2
    copying lib/_range.py -&gt; build/lib.macosx-10.15-x86_64-3.7/psycopg2
    copying lib/_ipaddress.py -&gt; build/lib.macosx-10.15-x86_64-3.7/psycopg2
    copying lib/_lru_cache.py -&gt; build/lib.macosx-10.15-x86_64-3.7/psycopg2
    copying lib/__init__.py -&gt; build/lib.macosx-10.15-x86_64-3.7/psycopg2
    copying lib/extensions.py -&gt; build/lib.macosx-10.15-x86_64-3.7/psycopg2
    copying lib/errors.py -&gt; build/lib.macosx-10.15-x86_64-3.7/psycopg2
    copying lib/sql.py -&gt; build/lib.macosx-10.15-x86_64-3.7/psycopg2
    copying lib/pool.py -&gt; build/lib.macosx-10.15-x86_64-3.7/psycopg2
    running build_ext
    building 'psycopg2._psycopg' extension
    creating build/temp.macosx-10.15-x86_64-3.7
    creating build/temp.macosx-10.15-x86_64-3.7/psycopg
    clang -Wno-unused-result -Wsign-compare -Wunreachable-code -fno-common -dynamic -DNDEBUG -g -fwrapv -O3 -Wall -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk/usr/include -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk/System/Library/Frameworks/Tk.framework/Versions/8.5/Headers -DPSYCOPG_VERSION=2.8.5 (dt dec pq3 ext lo64) -DPG_VERSION_NUM=120002 -DHAVE_LO64=1 -I/usr/local/include -I/usr/local/opt/openssl@1.1/include -I/usr/local/opt/sqlite/include -I/Users/nicolasrizzoehrenbock/Documents/ContactBook/venv/include -I/usr/local/opt/python/Frameworks/Python.framework/Versions/3.7/include/python3.7m -I. -I/usr/local/include -I/usr/local/include/postgresql/server -c psycopg/psycopgmodule.c -o build/temp.macosx-10.15-x86_64-3.7/psycopg/psycopgmodule.o
    In file included from psycopg/psycopgmodule.c:28:
    In file included from ./psycopg/psycopg.h:35:
    In file included from /Users/nicolasrizzoehrenbock/Documents/ContactBook/venv/include/Python.h:8:
    /Users/nicolasrizzoehrenbock/Documents/ContactBook/venv/include/pyconfig.h:59:10: fatal error: 'io.h' file not found
    #include &lt;io.h&gt;
             ^~~~~~
    1 error generated.
  
    It appears you are missing some prerequisite to build the package from source.
  
    You may install a binary package by installing 'psycopg2-binary' from PyPI.
    If you want to install psycopg2 from source, please install the packages
    required for the build and try again.
  
    For further information please check the 'doc/src/install.rst' file (also at
    &lt;https://www.psycopg.org/docs/install.html&gt;).
  
    error: command 'clang' failed with exit status 1
    ----------------------------------------
    ERROR: Failed building wheel for psycopg2
    Running setup.py clean for psycopg2
  Failed to build psycopg2
  Installing collected packages: psycopg2
      Running setup.py install for psycopg2 ... error
      ERROR: Command errored out with exit status 1:
       command: /Users/nicolasrizzoehrenbock/Documents/ContactBook/venv/bin/python -u -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/private/var/folders/yj/3jfym00d7r3_f9_jmkrt999r0000gn/T/pip-install-mpy9u7el/psycopg2/setup.py'"'"'; __file__='"'"'/private/var/folders/yj/3jfym00d7r3_f9_jmkrt999r0000gn/T/pip-install-mpy9u7el/psycopg2/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' install --record /private/var/folders/yj/3jfym00d7r3_f9_jmkrt999r0000gn/T/pip-record-3cminrp4/install-record.txt --single-version-externally-managed --compile --install-headers /Users/nicolasrizzoehrenbock/Documents/ContactBook/venv/include/site/python3.7/psycopg2
           cwd: /private/var/folders/yj/3jfym00d7r3_f9_jmkrt999r0000gn/T/pip-install-mpy9u7el/psycopg2/
      Complete output (42 lines):
      running install
      running build
      running build_py
      creating build
      creating build/lib.macosx-10.15-x86_64-3.7
      creating build/lib.macosx-10.15-x86_64-3.7/psycopg2
      copying lib/_json.py -&gt; build/lib.macosx-10.15-x86_64-3.7/psycopg2
      copying lib/extras.py -&gt; build/lib.macosx-10.15-x86_64-3.7/psycopg2
      copying lib/compat.py -&gt; build/lib.macosx-10.15-x86_64-3.7/psycopg2
      copying lib/errorcodes.py -&gt; build/lib.macosx-10.15-x86_64-3.7/psycopg2
      copying lib/tz.py -&gt; build/lib.macosx-10.15-x86_64-3.7/psycopg2
      copying lib/_range.py -&gt; build/lib.macosx-10.15-x86_64-3.7/psycopg2
      copying lib/_ipaddress.py -&gt; build/lib.macosx-10.15-x86_64-3.7/psycopg2
      copying lib/_lru_cache.py -&gt; build/lib.macosx-10.15-x86_64-3.7/psycopg2
      copying lib/__init__.py -&gt; build/lib.macosx-10.15-x86_64-3.7/psycopg2
      copying lib/extensions.py -&gt; build/lib.macosx-10.15-x86_64-3.7/psycopg2
      copying lib/errors.py -&gt; build/lib.macosx-10.15-x86_64-3.7/psycopg2
      copying lib/sql.py -&gt; build/lib.macosx-10.15-x86_64-3.7/psycopg2
      copying lib/pool.py -&gt; build/lib.macosx-10.15-x86_64-3.7/psycopg2
      running build_ext
      building 'psycopg2._psycopg' extension
      creating build/temp.macosx-10.15-x86_64-3.7
      creating build/temp.macosx-10.15-x86_64-3.7/psycopg
      clang -Wno-unused-result -Wsign-compare -Wunreachable-code -fno-common -dynamic -DNDEBUG -g -fwrapv -O3 -Wall -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk/usr/include -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk/System/Library/Frameworks/Tk.framework/Versions/8.5/Headers -DPSYCOPG_VERSION=2.8.5 (dt dec pq3 ext lo64) -DPG_VERSION_NUM=120002 -DHAVE_LO64=1 -I/usr/local/include -I/usr/local/opt/openssl@1.1/include -I/usr/local/opt/sqlite/include -I/Users/nicolasrizzoehrenbock/Documents/ContactBook/venv/include -I/usr/local/opt/python/Frameworks/Python.framework/Versions/3.7/include/python3.7m -I. -I/usr/local/include -I/usr/local/include/postgresql/server -c psycopg/psycopgmodule.c -o build/temp.macosx-10.15-x86_64-3.7/psycopg/psycopgmodule.o
      In file included from psycopg/psycopgmodule.c:28:
      In file included from ./psycopg/psycopg.h:35:
      In file included from /Users/nicolasrizzoehrenbock/Documents/ContactBook/venv/include/Python.h:8:
      /Users/nicolasrizzoehrenbock/Documents/ContactBook/venv/include/pyconfig.h:59:10: fatal error: 'io.h' file not found
      #include &lt;io.h&gt;
               ^~~~~~
      1 error generated.
  
      It appears you are missing some prerequisite to build the package from source.
  
      You may install a binary package by installing 'psycopg2-binary' from PyPI.
      If you want to install psycopg2 from source, please install the packages
      required for the build and try again.
  
      For further information please check the 'doc/src/install.rst' file (also at
      &lt;https://www.psycopg.org/docs/install.html&gt;).
  
      error: command 'clang' failed with exit status 1
      ----------------------------------------
  ERROR: Command errored out with exit status 1: /Users/nicolasrizzoehrenbock/Documents/ContactBook/venv/bin/python -u -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/private/var/folders/yj/3jfym00d7r3_f9_jmkrt999r0000gn/T/pip-install-mpy9u7el/psycopg2/setup.py'"'"'; __file__='"'"'/private/var/folders/yj/3jfym00d7r3_f9_jmkrt999r0000gn/T/pip-install-mpy9u7el/psycopg2/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' install --record /private/var/folders/yj/3jfym00d7r3_f9_jmkrt999r0000gn/T/pip-record-3cminrp4/install-record.txt --single-version-externally-managed --compile --install-headers /Users/Documents/venv/include/site/python3.7/psycopg2 Check the logs for full command output.
  </code></pre>
  
  <p>I tried doing <code>pip install psycopg2-binary</code>but i have it already installed. I also tried in already asked questions but nothing worked. Thanks in advance</p>