title: OSError: Could not open VISA library
body: <p>I have just installed pyvisa on my mac with</p>
  
  <pre><code>$ pip install pyvisa
  </code></pre>
  
  <p>But when I was to test it using IDLE like this:</p>
  
  <pre><code>import visa
  rm = visa.ResourceManager()
  </code></pre>
  
  <p>I got this:</p>
  
  <pre><code>    Traceback (most recent call last):
    File "&lt;pyshell#3&gt;", line 1, in &lt;module&gt;
      rm = visa.ResourceManager()
    File "/Users/siyuqi/Library/Python/2.7/lib/python/site-packages/pyvisa/highlevel.py", line 1488, in __new__
      visa_library = open_visa_library(visa_library)
    File "/Users/siyuqi/Library/Python/2.7/lib/python/site-packages/pyvisa/highlevel.py", line 1460, in open_visa_library
      return cls(argument)
    File "/Users/siyuqi/Library/Python/2.7/lib/python/site-packages/pyvisa/highlevel.py", line 96, in __new__
      raise OSError('Could not open VISA library:\n' + '\n'.join(errs))
  OSError: Could not open VISA library:
  </code></pre>
  
  <p>If I try 'pip install' in Terminal again, I will get the following result:</p>
  
  <pre><code>Requirement already satisfied (use --upgrade to upgrade): pyvisa in ./Library/Python/2.7/lib/python/site-packages
  Requirement already satisfied (use --upgrade to upgrade): enum34 in ./Library/Python/2.7/lib/python/site-packages (from pyvisa)
  </code></pre>
  
  <p>Could anybody please kindly help me solve my problem? Thanks!</p>