title: installing regex on python 2.7 fails with exit status 1
body: <p>I want to use the <a href="https://github.com/jaijuneja/PyTLDR" rel="nofollow noreferrer">PyTLDR</a>. Someone in the <a href="https://github.com/jaijuneja/PyTLDR/issues/3" rel="nofollow noreferrer">issue section</a> on GitHub  stated that the module was written in Python 2. Therefore, I set up a Python 2.7 environment for this project.
  My pip version is 20.3 which should still work for Python 2 modules.
  While installing the PyTLDR module via <code>pip install pytldr</code> I got the following error message:</p>
  <pre><code>[33mDEPRECATION: Python 2.7 reached the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 is no longer maintained. pip 21.0 will drop support for Python 2.7 in January 2021. More details about Python 2 support in pip can be found at https://pip.pypa.io/en/latest/development/release-process/#python-2-support pip 21.0 will remove support for this functionality.[0m
  Processing /home/zyko/.cache/pip/wheels/ba/d8/92/30e242ea7de520ed1eaf44ba37f7e73a2ac1e6b4e305b99e74/PyTLDR-0.1.4-py2-none-any.whl
  Processing /home/zyko/.cache/pip/wheels/c7/b1/76/54236c34227a12d32dc9cfe18731976baf8950d8a5aabaea6c/nltk-3.5-py2-none-any.whl
  Collecting numpy&gt;=1.8.0
    Using cached numpy-1.16.6-cp27-cp27mu-manylinux1_x86_64.whl (17.0 MB)
  Collecting scipy&gt;=0.13.2
    Using cached scipy-1.2.3-cp27-cp27mu-manylinux1_x86_64.whl (24.8 MB)
  Processing /home/zyko/.cache/pip/wheels/df/80/48/106e63760ff0dcd3658613d93c1ecf64301b9261172f2c1acf/networkx-2.2-py2.py3-none-any.whl
  Processing /home/zyko/.cache/pip/wheels/09/dd/9a/3eff624a1731b5df39e1a946425532b9c1e0330c4e705a629d/goose_extractor-1.0.25-py2-none-any.whl
  Collecting scikit-learn&gt;=0.15.2
    Using cached scikit_learn-0.20.4-cp27-cp27mu-manylinux1_x86_64.whl (5.5 MB)
  Requirement already satisfied: tqdm in ./venv/lib/python2.7/site-packages (from nltk&gt;=3.0.0-&gt;pytldr) (4.61.1)
  Requirement already satisfied: click in ./venv/lib/python2.7/site-packages (from nltk&gt;=3.0.0-&gt;pytldr) (7.1.2)
  Requirement already satisfied: joblib in ./venv/lib/python2.7/site-packages (from nltk&gt;=3.0.0-&gt;pytldr) (0.14.1)
  Collecting regex
    Using cached regex-2021.4.4.tar.gz (693 kB)
  Requirement already satisfied: decorator&gt;=4.3.0 in ./venv/lib/python2.7/site-packages (from networkx&gt;=1.9.1-&gt;pytldr) (4.4.2)
  Collecting cssselect
    Using cached cssselect-1.1.0-py2.py3-none-any.whl (16 kB)
  Processing /home/zyko/.cache/pip/wheels/4b/8e/29/f0d0909969495c5f279c6cba4ceca07db79a0f7bb54f3f087b/jieba-0.42.1-py2-none-any.whl
  Collecting beautifulsoup
    Using cached BeautifulSoup-3.2.2-py2-none-any.whl (32 kB)
  Collecting lxml
    Using cached lxml-4.6.3-cp27-cp27mu-manylinux1_x86_64.whl (5.5 MB)
  Collecting Pillow
    Using cached Pillow-6.2.2-cp27-cp27mu-manylinux1_x86_64.whl (2.1 MB)
  Building wheels for collected packages: regex
    Building wheel for regex (setup.py) ... [?25l- error
  [31m  ERROR: Command errored out with exit status 1:
     command: /home/zyko/PycharmProjects/PyTLDR/venv/bin/python2.7 -u -c 'import sys, setuptools, tokenize; sys.argv[0] = '&quot;'&quot;'/tmp/pip-install-9Mtbpc/regex/setup.py'&quot;'&quot;'; __file__='&quot;'&quot;'/tmp/pip-install-9Mtbpc/regex/setup.py'&quot;'&quot;';f=getattr(tokenize, '&quot;'&quot;'open'&quot;'&quot;', open)(__file__);code=f.read().replace('&quot;'&quot;'\r\n'&quot;'&quot;', '&quot;'&quot;'\n'&quot;'&quot;');f.close();exec(compile(code, __file__, '&quot;'&quot;'exec'&quot;'&quot;'))' bdist_wheel -d /tmp/pip-wheel-URFXXo
         cwd: /tmp/pip-install-9Mtbpc/regex/
    Complete output (20 lines):
    running bdist_wheel
    running build
    running build_py
    creating build
    creating build/lib.linux-x86_64-2.7
    creating build/lib.linux-x86_64-2.7/regex
    copying regex_2/__init__.py -&gt; build/lib.linux-x86_64-2.7/regex
    copying regex_2/regex.py -&gt; build/lib.linux-x86_64-2.7/regex
    copying regex_2/_regex_core.py -&gt; build/lib.linux-x86_64-2.7/regex
    copying regex_2/test_regex.py -&gt; build/lib.linux-x86_64-2.7/regex
    running build_ext
    building 'regex._regex' extension
    creating build/temp.linux-x86_64-2.7
    creating build/temp.linux-x86_64-2.7/regex_2
    x86_64-linux-gnu-gcc -pthread -fno-strict-aliasing -Wdate-time -D_FORTIFY_SOURCE=2 -g -fdebug-prefix-map=/build/python2.7-QDqKfA/python2.7-2.7.18=. -fstack-protector-strong -Wformat -Werror=format-security -fPIC -I/usr/include/python2.7 -c regex_2/_regex.c -o build/temp.linux-x86_64-2.7/regex_2/_regex.o
    regex_2/_regex.c:50:10: fatal error: Python.h: No such file or directory
       50 | #include &quot;Python.h&quot;
          |          ^~~~~~~~~~
    compilation terminated.
    error: command 'x86_64-linux-gnu-gcc' failed with exit status 1
    ----------------------------------------[0m
  [31m  ERROR: Failed building wheel for regex[0m
  [?25h  Running setup.py clean for regex
  Failed to build regex
  Installing collected packages: regex, nltk, numpy, scipy, networkx, cssselect, jieba, beautifulsoup, lxml, Pillow, goose-extractor, scikit-learn, pytldr
      Running setup.py install for regex ... [?25l- error
  [31m    ERROR: Command errored out with exit status 1:
       command: /home/zyko/PycharmProjects/PyTLDR/venv/bin/python2.7 -u -c 'import sys, setuptools, tokenize; sys.argv[0] = '&quot;'&quot;'/tmp/pip-install-9Mtbpc/regex/setup.py'&quot;'&quot;'; __file__='&quot;'&quot;'/tmp/pip-install-9Mtbpc/regex/setup.py'&quot;'&quot;';f=getattr(tokenize, '&quot;'&quot;'open'&quot;'&quot;', open)(__file__);code=f.read().replace('&quot;'&quot;'\r\n'&quot;'&quot;', '&quot;'&quot;'\n'&quot;'&quot;');f.close();exec(compile(code, __file__, '&quot;'&quot;'exec'&quot;'&quot;'))' install --record /tmp/pip-record-pYEqUQ/install-record.txt --single-version-externally-managed --compile --install-headers /home/zyko/PycharmProjects/PyTLDR/venv/include/site/python2.7/regex
           cwd: /tmp/pip-install-9Mtbpc/regex/
      Complete output (20 lines):
      running install
      running build
      running build_py
      creating build
      creating build/lib.linux-x86_64-2.7
      creating build/lib.linux-x86_64-2.7/regex
      copying regex_2/__init__.py -&gt; build/lib.linux-x86_64-2.7/regex
      copying regex_2/regex.py -&gt; build/lib.linux-x86_64-2.7/regex
      copying regex_2/_regex_core.py -&gt; build/lib.linux-x86_64-2.7/regex
      copying regex_2/test_regex.py -&gt; build/lib.linux-x86_64-2.7/regex
      running build_ext
      building 'regex._regex' extension
      creating build/temp.linux-x86_64-2.7
      creating build/temp.linux-x86_64-2.7/regex_2
      x86_64-linux-gnu-gcc -pthread -fno-strict-aliasing -Wdate-time -D_FORTIFY_SOURCE=2 -g -fdebug-prefix-map=/build/python2.7-QDqKfA/python2.7-2.7.18=. -fstack-protector-strong -Wformat -Werror=format-security -fPIC -I/usr/include/python2.7 -c regex_2/_regex.c -o build/temp.linux-x86_64-2.7/regex_2/_regex.o
      regex_2/_regex.c:50:10: fatal error: Python.h: No such file or directory
         50 | #include &quot;Python.h&quot;
            |          ^~~~~~~~~~
      compilation terminated.
      error: command 'x86_64-linux-gnu-gcc' failed with exit status 1
      ----------------------------------------[0m
  [31mERROR: Command errored out with exit status 1: /home/zyko/PycharmProjects/PyTLDR/venv/bin/python2.7 -u -c 'import sys, setuptools, tokenize; sys.argv[0] = '&quot;'&quot;'/tmp/pip-install-9Mtbpc/regex/setup.py'&quot;'&quot;'; __file__='&quot;'&quot;'/tmp/pip-install-9Mtbpc/regex/setup.py'&quot;'&quot;';f=getattr(tokenize, '&quot;'&quot;'open'&quot;'&quot;', open)(__file__);code=f.read().replace('&quot;'&quot;'\r\n'&quot;'&quot;', '&quot;'&quot;'\n'&quot;'&quot;');f.close();exec(compile(code, __file__, '&quot;'&quot;'exec'&quot;'&quot;'))' install --record /tmp/pip-record-pYEqUQ/install-record.txt --single-version-externally-managed --compile --install-headers /home/zyko/PycharmProjects/PyTLDR/venv/include/site/python2.7/regex Check the logs for full command output.[0m
  [33mWARNING: You are using pip version 20.3; however, version 20.3.4 is available.
  You should consider upgrading via the '/home/zyko/PycharmProjects/PyTLDR/venv/bin/python2.7 -m pip install --upgrade pip' command.[0m
  [?25h
  </code></pre>
  <p>It looks like the regex module can not be installed. A manual <code>pip install regex</code> throws the same error message.
  How can I get regex to work within the old Python 2.7 version and subsequently get the PyTLDR module to work properly?</p>