selenium: unable to access geckodriver

Question

I dowloaded the latest versions of both selenium and geckodriver. I did the following:

bash

cp Downloads/geckodriver /usr/local/bin/
PATH=$PATH:/usr/local/bin/geckodriver

python

from selenium import webdriver
browser = webdriver.Firefox()

error

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/chris/anaconda/lib/python2.7/site-packages/selenium/webdriver/firefox/webdriver.py", line 140, in __init__
    self.service.start()
  File "/Users/chris/anaconda/lib/python2.7/site-packages/selenium/webdriver/common/service.py", line 74, in start
    stdout=self.log_file, stderr=self.log_file)
  File "/Users/chris/anaconda/lib/python2.7/subprocess.py", line 710, in __init__
    errread, errwrite)
  File "/Users/chris/anaconda/lib/python2.7/subprocess.py", line 1335, in _execute_child
    raise child_exception
OSError: [Errno 8] Exec format error

UPDATE

I did the same thing with chrome web driver:

browser = webdriver.Chrome()

error

selenium.common.exceptions.WebDriverException: Message: unknown error: cannot find Chrome binary
  (Driver info: chromedriver=2.27.440174 (e97a722caafc2d3a8b807ee115bfb307f7d2cfd9),platform=Mac OS X 10.12.3 x86_64)

Is this something to do with specifying the path?? Really confused as I am inexperienced with bash