title: Error while installing Selenium in pip3
body: <p>I am attempting to install selenium, and yet there seems to be a problem:</p>
  
  <p>I ran pip3 install -U selenium, and I get:</p>
  
  <pre><code>    Exception:
  Traceback (most recent call last):
    File "/usr/local/lib/python3.5/site-packages/pip/basecommand.py", line 215, in main
      status = self.run(options, args)
    File "/usr/local/lib/python3.5/site-packages/pip/commands/install.py", line 317, in run
      prefix=options.prefix_path,
    File "/usr/local/lib/python3.5/site-packages/pip/req/req_set.py", line 742, in install
      **kwargs
    File "/usr/local/lib/python3.5/site-packages/pip/req/req_install.py", line 831, in install
      self.move_wheel_files(self.source_dir, root=root, prefix=prefix)
    File "/usr/local/lib/python3.5/site-packages/pip/req/req_install.py", line 1032, in move_wheel_files
      isolated=self.isolated,
    File "/usr/local/lib/python3.5/site-packages/pip/wheel.py", line 378, in move_wheel_files
      clobber(source, dest, False, fixer=fixer, filter=filter)
    File "/usr/local/lib/python3.5/site-packages/pip/wheel.py", line 317, in clobber
      ensure_dir(destdir)
    File "/usr/local/lib/python3.5/site-packages/pip/utils/__init__.py", line 83, in ensure_dir
      os.makedirs(path)
    File "/usr/local/Cellar/python3/3.5.2_2/Frameworks/Python.framework/Versions/3.5/lib/python3.5/os.py", line 231, in makedirs
      makedirs(head, mode, exist_ok)
    File "/usr/local/Cellar/python3/3.5.2_2/Frameworks/Python.framework/Versions/3.5/lib/python3.5/os.py", line 231, in makedirs
      makedirs(head, mode, exist_ok)
    File "/usr/local/Cellar/python3/3.5.2_2/Frameworks/Python.framework/Versions/3.5/lib/python3.5/os.py", line 231, in makedirs
  makedirs(head, mode, exist_ok)
    File "/usr/local/Cellar/python3/3.5.2_2/Frameworks/Python.framework/Versions/3.5/lib/python3.5/os.py", line 241, in makedirs
      mkdir(name, mode)
  PermissionError: [Errno 13] Permission denied: '/usr/local/selenium'
  </code></pre>
  
  <p>Despite this message, I can proceed and run selenium in python3, and a command like</p>
  
  <pre><code>from selenium import web driver
  browser = webdriver.Firefox()
  </code></pre>
  
  <p>will return </p>
  
  <pre><code>Traceback (most recent call last):
    File "/usr/local/lib/python3.5/site-packages/selenium/webdriver/common/service.py", line 64, in start
  stdout=self.log_file, stderr=self.log_file)
    File "/usr/local/Cellar/python3/3.5.2_2/Frameworks/Python.framework/Versions/3.5/lib/python3.5/subprocess.py", line 947, in __init__
  restore_signals, start_new_session)
    File "/usr/local/Cellar/python3/3.5.2_2/Frameworks/Python.framework/Versions/3.5/lib/python3.5/subprocess.py", line 1551, in _execute_child
  raise child_exception_type(errno_num, err_msg)
  FileNotFoundError: [Errno 2] No such file or directory: 'geckodriver'
  
  During handling of the above exception, another exception occurred:
  
  Traceback (most recent call last):
    File "&lt;stdin&gt;", line 1, in &lt;module&gt;
    File "/usr/local/lib/python3.5/site-packages/selenium/webdriver/firefox/webdriver.py", line 135, in __init__
  self.service.start()
    File "/usr/local/lib/python3.5/site-packages/selenium/webdriver/common/service.py", line 71, in start
  os.path.basename(self.path), self.start_error_message)
  selenium.common.exceptions.WebDriverException: Message: 'geckodriver' executable needs to be in PATH.
  </code></pre>
  
  <p>What do I need to do?</p>