Webdriver in Python - Executing Function from External Script

Question

How do I execute a function located in an external JavaScript using webdriver in python?

The JavaScript is used to overwrite JavaScripts internal DateTime object to give an altered browser time for unit testing. I like to use sinonfaketimers.js for this purpose. (But would also go with alternatives like TimeShift.js) Links: http://sinonjs.org/docs/#clock , https://github.com/plaa/TimeShift-js

So I wrote the following python code, which calls the JavaScript itself but not the respective function:

driver = webdriver.Firefox()    
driver.get("http://google.com")
driver.execute_script(open("./sinon_timers.js").read()) 
# some code here to test shift in time    
driver.quit()

As far as I understand this matter correctly all I need to do in order to make this work is to run the respective JavaScript function with the correct arguments. I assume passing the arguments could be done by building a suitable string like:

     driver.execute_script("function('" + argument_var + "');")

The actual function inside the JavaScript sinon_timers.js is:

sinon.timers = {
    setTimeout: setTimeout,
    clearTimeout: clearTimeout,
    setImmediate: (typeof setImmediate !== "undefined" ? setImmediate : undefined),
    clearImmediate: (typeof clearImmediate !== "undefined" ? clearImmediate: undefined),
    setInterval: setInterval,
    clearInterval: clearInterval,
    Date: Date
};

The full length script can be found at sinonjs.org:

http://sinonjs.org/releases/sinon-timers-1.12.1.js

But I am not sure about the syntax of calling the function sinon.timers in sinon_timers.js. How do I do that?

UPDATE:

Sainath Motlakunta suggested a solution. Unfortunately it doesn't work. But maybe we are closer a step to cracking the puzzle:

driver = webdriver.Firefox()    
driver.get("https://duckduckgo.com")    
driver.execute_script(open("./sinon_timers.js").read())  # <- is this line important?
driver.execute_script("var clock = sinon.useFakeTimers(12345);")    
driver.quit()

This yields: selenium.common.exceptions.WebDriverException: Message: sinon is not defined

Full traceback:

Traceback (most recent call last):
  File "/path/sinonJS_test.py", line 47, in <module>
    sinon_test()
  File "/path/sinonJS_test.py", line 37, in sinon_test
    driver.execute_script("var clock = sinon.useFakeTimers(12345);")
  File "/usr/local/lib/python2.7/dist-packages/selenium/webdriver/remote/webdriver.py",     line 401, in execute_script
    {'script': script, 'args':converted_args})['value']
  File "/usr/local/lib/python2.7/dist-packages/selenium/webdriver/remote/webdriver.py",     line 173, in execute
    self.error_handler.check_response(response)
  File "/usr/local/lib/python2.7/dist-packages/selenium/webdriver/remote/errorhandler.py", line 166, in check_response
   raise exception_class(message, screen, stacktrace)
selenium.common.exceptions.WebDriverException: Message: sinon is not defined

Is there maybe some useful information in this post, asking exactly the same question?: https://sqa.stackexchange.com/questions/8838/faking-system-time-date-with-selenium-webdriver

The proposed solution sketched is:

1. List item Inject/Add the mocking framework during tests runs

2. Mock the Date object with the JavaScript Executor

3. Set the timezone

4. Run tests