title: How to use requirements.txt to install all dependencies in a python project
body: <p>I am new to python. Recently I got a project written by python and it requires some installation. I run below command to install but got an error.</p>
  
  <pre><code># pip install requirements.txt 
  Collecting requirements.txt
    Could not find a version that satisfies the requirement requirements.txt (from versions: )
  No matching distribution found for requirements.txt
  </code></pre>
  
  <p>I searched on google and found this link <code>http://stackoverflow.com/questions/28167987/python-pip-trouble-installing-from-requirements-txt</code> but I don't quite understand what the solution in that post.</p>
  
  <p>Below is my requirements.txt file:</p>
  
  <pre><code># cat requirements.txt 
  ordereddict==1.1
  argparse==1.2.1
  python-dateutil==2.2
  matplotlib==1.3.1
  nose==1.3.0
  numpy==1.8.0
  pymongo==3.3.0
  psutil&gt;=2.0
  </code></pre>
  
  <p>Is there a easy way to install all required dependencies in this python project? </p>
  
  <p><strong>EDIT1</strong></p>
  
  <p>Below is the output from <code>pip3 install -r requirements.txt</code>.</p>
  
  <pre><code># pip3 install -r requirements.txt 
  Requirement already satisfied: ordereddict==1.1 in /usr/local/lib/python3.5/dist-packages (from -r requirements.txt (line 1))
  Collecting argparse==1.2.1 (from -r requirements.txt (line 2))
    Using cached argparse-1.2.1.tar.gz
  Collecting python-dateutil==2.2 (from -r requirements.txt (line 3))
    Using cached python-dateutil-2.2.tar.gz
  Collecting matplotlib==1.3.1 (from -r requirements.txt (line 4))
    Using cached matplotlib-1.3.1.tar.gz
      Complete output from command python setup.py egg_info:
      ============================================================================
      Edit setup.cfg to change the build options
  
      BUILDING MATPLOTLIB
                  matplotlib: yes [1.3.1]
                      python: yes [3.5.2 (default, Nov 17 2016, 17:05:23)  [GCC
                              5.4.0 20160609]]
                    platform: yes [linux]
  
      REQUIRED DEPENDENCIES AND EXTENSIONS
                       numpy: yes [version 1.11.3]
                    dateutil: yes [using dateutil version 2.6.0]
                     tornado: yes [tornado was not found. It is required for the
                              WebAgg backend. pip/easy_install may attempt to
                              install it after matplotlib.]
                   pyparsing: yes [using pyparsing version 2.1.10]
                       pycxx: yes [Official versions of PyCXX are not compatible
                              with Python 3.x.  Using local copy]
                      libagg: yes [pkg-config information for 'libagg' could not
                              be found. Using local copy.]
                    freetype: no  [The C/C++ header for freetype2 (ft2build.h)
                              could not be found.  You may need to install the
                              development package.]
                         png: yes [pkg-config information for 'libpng' could not
                              be found. Using unknown version.]
  
      OPTIONAL SUBPACKAGES
                 sample_data: yes [installing]
                    toolkits: yes [installing]
                       tests: yes [using nose version 1.3.7]
  
      OPTIONAL BACKEND EXTENSIONS
                      macosx: no  [Mac OS-X only]
                      qt4agg: no  [PyQt4 not found]
                     gtk3agg: no  [gtk3agg backend does not work on Python 3]
                   gtk3cairo: no  [Requires cairo to be installed.]
                      gtkagg: no  [Requires pygtk]
                       tkagg: no  [TKAgg requires Tkinter.]
                       wxagg: no  [requires wxPython]
                         gtk: no  [Requires pygtk]
                         agg: yes [installing]
                       cairo: no  [cairo not found]
                   windowing: no  [Microsoft Windows only]
  
      OPTIONAL LATEX DEPENDENCIES
                      dvipng: no
                 ghostscript: no
                       latex: no
                     pdftops: no
  
      ============================================================================
                              * The following required packages can not be built:
                              * freetype
  
      ----------------------------------------
  Command "python setup.py egg_info" failed with error code 1 in /tmp/pip-build-don4ne_2/matplotlib/
  </code></pre>
  
  <p>I have already installed <code>libfreetype6-dev</code> but the pip command still reports missing this dependency.</p>
  
  <pre><code># apt-get install libfreetype6-dev
  Reading package lists... Done
  Building dependency tree       
  Reading state information... Done
  libfreetype6-dev is already the newest version (2.6.1-0.1ubuntu2).
  0 upgraded, 0 newly installed, 0 to remove and 4 not upgraded.
  </code></pre>