title: "no such option: --allow-all-external" when deploying a Django app to Heroku with Anaconda
body: <p>I use Django 1.11.20 and Python 2.7. My app is deployed with Heroku.</p>
  
  <p>As I need NumPy / SciPy and Heroku has a slug size limited to 500Mb, I am using Anaconda through the three following Heroku buildpacks:</p>
  
  <ul>
  <li><code>https://github.com/kennethreitz/conda-buildpack</code></li>
  <li><code>https://github.com/cyberdelia/heroku-geo-buildpack.git</code></li>
  <li><code>heroku/python</code></li>
  </ul>
  
  <p>The site has been working perfectly for the last year and hadn't been updated it for a few months.</p>
  
  <p>I made some minor changes to the site recently and I got the following error when deploying it to Heroku.</p>
  
  <p>I don't understand what is the issue exactly.</p>
  
  <p>Any clue?</p>
  
  <pre><code>        -----&gt; Deleting 0 files matching .slugignore patterns.
          -----&gt; Python/Conda app detected
          added pinned file in /app/.heroku/miniconda/conda-meta/pinned
          Collecting package metadata: ...working... done
          Solving environment: ...working... done
          ## Package Plan ##
            environment location: /app/.heroku/miniconda
            added / updated specs:
              - nomkl
          The following packages will be downloaded:
              package                    |            build
              ---------------------------|-----------------
              nomkl-3.0                  |                0          48 KB
              ------------------------------------------------------------
                                                     Total:          48 KB
          The following packages will be UPDATED:
            nomkl                                               1.0-0 --&gt; 3.0-0
          Proceed ([y]/n)? 
          Downloading and Extracting Packages
          Preparing transaction: ...working... done
          Verifying transaction: ...working... done
          Executing transaction: ...working... done
          -----&gt; Installing dependencies using Conda
                 Collecting package metadata: ...working... done
                 Solving environment: ...working... 
                 The environment is inconsistent, please check the package plan             carefully
             The following packages are causing the inconsistency:
  
                   - defaults/linux-64::readline==7.0=h7b6447c_5
                   - defaults/linux-64::zlib==1.2.11=h7b6447c_3
                   - defaults/linux-64::python==2.7.15=h9bab390_6
                   - defaults/linux-64::scipy==0.17.1=np111py27_nomkl_0
                   - defaults/linux-64::pycparser==2.18=py27_0
                   - defaults/linux-64::ncurses==6.1=he6710b0_1
                   - defaults/linux-64::pysocks==1.6.7=py27he2db6d2_1
                   - defaults/linux-64::pycosat==0.6.3=py27ha4109ae_0
                   - defaults/linux-64::sqlite==3.26.0=h7b6447c_0
                   - defaults/linux-64::pycrypto==2.6.1=py27_0
                   - defaults/linux-64::openssl==1.1.1c=h7b6447c_1
                   - defaults/linux-64::libgcc-ng==8.2.0=hdf63c60_1
                   - defaults/linux-64::scikit-learn==0.17.1=np111py27_nomkl_1
                   - defaults/linux-64::six==1.10.0=py27_0
                   - defaults/linux-64::numpy==1.11.0=py27_nomkl_1
                   - defaults/linux-64::certifi==2019.3.9=py27_0
                   - defaults/linux-64::asn1crypto==0.22.0=py27_0
                   - defaults/linux-64::wheel==0.29.0=py27_0
                   - defaults/linux-64::urllib3==1.22=py27ha55213b_0
                   - defaults/linux-64::packaging==16.8=py27_0
                   - defaults/linux-64::cryptography==2.5=py27h1ba5d50_0
                   - defaults/linux-64::pyparsing==2.2.0=py27_0
                   - defaults/linux-64::ruamel_yaml==0.11.14=py27_1
                   - defaults/linux-64::libedit==3.1.20181209=hc058e9b_0
                   - defaults/linux-64::idna==2.6=py27_0
                   - defaults/linux-64::pyopenssl==17.0.0=py27_0
                   - defaults/linux-64::conda==4.6.14=py27_0
                   - defaults/linux-64::ipaddress==1.0.18=py27_0
                   - defaults/linux-64::cffi==1.10.0=py27_0
                   - defaults/linux-64::enum34==1.1.6=py27_0
                   - defaults/linux-64::requests==2.18.4=py27hc5b0589_1
                   - defaults/linux-64::tk==8.6.8=hbc83047_0
                   - defaults/linux-64::pyyaml==3.11=py27_1
                   - defaults/linux-64::pip==9.0.1=py27_1
                   - defaults/linux-64::chardet==3.0.4=py27hfa10054_1
                   - defaults/linux-64::futures==3.2.0=py27h7b459c0_0
                   - defaults/linux-64::setuptools==36.5.0=py27h68b189e_0
                 done
              ==&gt; WARNING: A newer version of conda exists. &lt;==
            current version: 4.6.14
            latest version: 4.7.10
      Please update conda by running
          $ conda update -n base -c defaults conda
  
             ## Package Plan ##
  
               environment location: /app/.heroku/miniconda
  
               added / updated specs:
                 - nomkl==1.0=0
                 - numpy==1.11.0=py27_nomkl_1
                 - scikit-learn==0.17.1=np111py27_nomkl_1
                 - scipy==0.17.1=np111py27_nomkl_0
  
  
             The following packages will be downloaded:
  
                 package                    |            build
             ---------------------------|-----------------
             _libgcc_mutex-0.1          |             main           3 KB
             certifi-2019.6.16          |           py27_0         154 KB
             libgcc-ng-9.1.0            |       hdf63c60_0         8.1 MB
             nomkl-1.0                  |                0          402 B
             pip-19.1.1                 |           py27_0         1.8 MB
             python-2.7.16              |       h9bab390_0        12.8 MB
             setuptools-41.0.1          |           py27_0         640 KB
             sqlite-3.29.0              |       h7b6447c_0         1.9 MB
             wheel-0.33.4               |           py27_0          39 KB
             ------------------------------------------------------------
                                                    Total:        25.4 MB
  
     The following NEW packages will be INSTALLED:
  
       _libgcc_mutex      pkgs/main/linux-64::_libgcc_mutex-0.1-main
  
     The following packages will be UPDATED:
  
       certifi                                   2019.3.9-py27_0 --&gt; 2019.6.16-py27_0
       libgcc-ng                                8.2.0-hdf63c60_1 --&gt; 9.1.0-hdf63c60_0
       pip                           pkgs/free::pip-9.0.1-py27_1 --&gt; pkgs/main::pip-19.1.1-py27_0
       python                                  2.7.15-h9bab390_6 --&gt; 2.7.16-h9bab390_0
       setuptools                          36.5.0-py27h68b189e_0 --&gt; 41.0.1-py27_0
       sqlite                                  3.26.0-h7b6447c_0 --&gt; 3.29.0-h7b6447c_0
       wheel                      pkgs/free::wheel-0.29.0-py27_0 --&gt; pkgs/main::wheel-0.33.4-py27_0
  
     The following packages will be DOWNGRADED:
  
       nomkl                                               3.0-0 --&gt; 1.0-0
  
  
  
     Downloading and Extracting Packages
  
     Preparing transaction: ...working... done
     Verifying transaction: ...working... done
     Executing transaction: ...working... done
  -----&gt; Installing dependencies using Pip
  Usage:   
    pip install [options] &lt;requirement specifier&gt; [package-index-options] ...
    pip install [options] -r &lt;requirements file&gt; [package-index-options] ...
    pip install [options] [-e] &lt;vcs project url&gt; ...
    pip install [options] [-e] &lt;local project path&gt; ...
    pip install [options] &lt;archive url/path&gt; ...
  no such option: --allow-all-external
   !     Push rejected, failed to compile Python/Conda app.
   !     Push failed
  </code></pre>