title: ImportError: No module named attr
body: <p>I have only very rudimentary experience in Python. I am trying to install the package <code>pyslim</code> (see <a href="https://pypi.org/project/pyslim/" rel="noreferrer">here on the pypi website</a>). I did</p>
  
  <pre><code>$ pip install pyslim
  
  Requirement already satisfied: pyslim in ./Library/Python/2.7/lib/python/site-packages/pyslim-0.1-py2.7.egg (0.1)
  Requirement already satisfied: msprime in /usr/local/lib/python2.7/site-packages (from pyslim) (0.6.1)
  Requirement already satisfied: attrs in /usr/local/lib/python2.7/site-packages (from pyslim) (16.3.0)
  Requirement already satisfied: svgwrite in /usr/local/lib/python2.7/site-packages (from msprime-&gt;pyslim) (1.1.12)
  Requirement already satisfied: jsonschema in /usr/local/lib/python2.7/site-packages (from msprime-&gt;pyslim) (2.6.0)
  Requirement already satisfied: six in /usr/local/lib/python2.7/site-packages (from msprime-&gt;pyslim) (1.10.0)
  Requirement already satisfied: numpy&gt;=1.7.0 in /usr/local/lib/python2.7/site-packages/numpy-1.10.4-py2.7-macosx-10.11-x86_64.egg (from msprime-&gt;pyslim) (1.10.4)
  Requirement already satisfied: h5py in /usr/local/lib/python2.7/site-packages (from msprime-&gt;pyslim) (2.8.0)
  Requirement already satisfied: pyparsing&gt;=2.0.1 in /usr/local/lib/python2.7/site-packages (from svgwrite-&gt;msprime-&gt;pyslim) (2.2.0)
  Requirement already satisfied: functools32; python_version == "2.7" in /usr/local/lib/python2.7/site-packages (from jsonschema-&gt;msprime-&gt;pyslim) (3.2.3.post2)
  </code></pre>
  
  <p>But when I open python and try to import <code>pyslim</code>, it fails</p>
  
  <pre><code>&gt; import pyslim
  
  Traceback (most recent call last):
    File "&lt;stdin&gt;", line 1, in &lt;module&gt;
    File "/Users/remi/Library/Python/2.7/lib/python/site-packages/pyslim-0.1-py2.7.egg/pyslim/__init__.py", line 4, in &lt;module&gt;
      from pyslim.slim_metadata import *       # NOQA
    File "/Users/remi/Library/Python/2.7/lib/python/site-packages/pyslim-0.1-py2.7.egg/pyslim/slim_metadata.py", line 1, in &lt;module&gt;
      import attr
  ImportError: No module named attr
  </code></pre>
  
  <p>So, I did </p>
  
  <pre><code>$ pip install attr
  Requirement already satisfied: attr in /usr/local/lib/python2.7/site-packages (0.3.1)
  </code></pre>
  
  <p>and </p>
  
  <pre><code>$ pip install attrs
  Requirement already satisfied: attrs in /usr/local/lib/python2.7/site-packages (16.3.0)
  </code></pre>
  
  <p>I restarted python and tried to import <code>pyslim</code> again but I keep receiving the same error message. I also tried to download and install the files from github by doing</p>
  
  <pre><code>$ git clone https://github.com/tskit-dev/pyslim.git
  $ cd pyslim
  $ python setup.py install --user
  </code></pre>
  
  <p>as indicated <a href="https://pypi.org/project/pyslim/" rel="noreferrer">here on the pypi website</a>. On this last line of code, I get a long output ending with </p>
  
  <pre><code>Download error on https://pypi.python.org/simple/: [SSL: TLSV1_ALERT_PROTOCOL_VERSION] tlsv1 alert protocol version (_ssl.c:590) -- Some packages may not be found!
  No local packages or download links found for attrs
  error: Could not find suitable distribution for Requirement.parse('attrs')
  </code></pre>
  
  <hr>
  
  <p>I am using <code>Python 2.7.10</code> on a <code>MAC OSX 10.11.6</code>. Not sure if it matter but I usually install things with homebrew. I am using <code>pip 18.1 from /usr/local/lib/python2.7/site-packages/pip (python 2.7)</code>.</p>
  
  <p><strong>Edit</strong></p>
  
  <pre><code>$ which python
     /usr/bin/python
  $ which pip
     /usr/local/bin/pip
  </code></pre>