title: pip - installation of sub-dependencies overrides other packages on requirements.txt
body: <p>my requirements file is like that : </p>
  
  <pre><code>https://github.com/sontek/pyramid_webassets/archive/38b0b9f9f4e36dc22b3a5c10eabf4d9228d97740.zip#egg=pyramid_webassets-0.0
  https://github.com/miracle2k/webassets/archive/334d55c6bcfd091cb2d984777daf943acde0d364.zip#egg=webassets-0.8.dev
  </code></pre>
  
  <p>when running <code>pip install -r requirements.txt</code> I want it to install the specific version of pyramid_webassets, and then the specific webassets version (0.8.dev) </p>
  
  <p>the problem is that pyramid_webassets have the webassets as sub-dependency, and it installs the latest of this package.</p>
  
  <p>so the output of pip freeze is </p>
  
  <pre><code>Chameleon==2.14
  Mako==0.9.1
  MarkupSafe==0.18
  PasteDeploy==1.5.2
  WebOb==1.3.1
  argparse==1.2.1
  pyramid==1.4.5
  pyramid-webassets==0.0
  repoze.lru==0.6
  translationstring==1.1
  venusian==1.0a8
  webassets==0.9
  wsgiref==0.1.2
  zope.deprecation==4.1.0
  zope.interface==4.0.5
  </code></pre>
  
  <p>you might notice that webassets version is the latest (0.9) though I specified the version I want (0.8.dev). </p>
  
  <p>I tried to reorder the list, adding the --upgrade flag- nothing helped. </p>
  
  <p>any idea how can I install it and still having the required version of webassets?</p>
  
  <p>Thanks.</p>
  
  <hr>
  
  <p>soultion:</p>
  
  <p>I found this commend useful: </p>
  
  <pre><code>cat requirements.txt | xargs -L1 pip install
  </code></pre>
  
  <p>that will install one by one the packages orderly</p>
  
  <p>but we should add --upgrade for the last package so it'll upgrade it.</p>