Today I learned a nifty trick in Python using list comprehensions. If you don’t know what list comprehensions are check out http://www.python.org/dev/peps/pep-0202/.

I recently had a scenario where I wanted to find the first item in a list that matched a single criteria. A basic loop can certainly do the job, as show below. In this example I want to return the first item in the list that is greater than the number 2.

a = [1, 2, 3, 4, 5]

def findFirstNumberGreaterThan2():
   result = None

   for i in a:
      if i > 2:
         result = i
         break

   return result

This works fine and all, but it is what Python folks call “pythonic”, and there is certainly a more concise way to handle this problem. Enter list comprehensions and the next() method. The next() method retrieves the next item from an iterable (is that a word??) and returns the value, or if it is not found the default value, found in the second argument, is returned. Let’s see this in action by reworking the previous example.

a = [1, 2, 3, 4, 5]

def findFirstNumberGreaterThan2():
   return next((i for i in a if i > 2), None)

Woah, that is pretty cool! The next() method takes two arguments. The first being an object that can be iterated over, and the second being a default value that is returned once the iterator is exhausted. The second argument is optional.

I definitely need to spend more time digging into the “pythonic” tricks of the trade. Happy coding!