Pythonic code: built-in functions

This post continues a series on “Pythonic” code. Pythonic code is code that fits well with the design of the Python language. The last post examined the property decorator as a technique to make beautiful classes. This fourth post will dive into Python’s built-in functions.

  1. The list comprehension
  2. The with statement
  3. The property decorator
  4. Built-in functions
  5. Using the standard library
  6. Leveraging packages

Built-in functions

A couple of years ago, I made a challenge for myself to read through all of Python’s standard library. Today, I would generally suggest that people don’t do that (for reasons I documented in a blog post about the readthrough experience).

Even with that caution, there is some documentation that you absolutely should read: the built-in functions reference.

The built-in functions are the set of functions that do not need to be imported. They are globally available in any Python source file. As of this writing (with Python 3.6.1 documentation), the set includes 68 functions. Some of these functions are extremely common and well known to proficient Python programmers like len and open. If you want to move from proficient to expert, using a majority of these functions will make your Python code far more Pythonic.

I’m going to describe a few of my favorites to give you an idea of what is available. Once you look at these examples, I’d really encourage you to read the built-in function reference so you can discover your own favorites!

Let’s look at these:

  • any
  • enumerate
  • print
  • range
  • sorted


The any function takes a list and returns True if anything in the list evaluates to True. This is a useful function for reducing a bunch of boolean checks into a single value. I think I’ve used any most often in cases where I’m checking permissions or other business rules.

>>> checks = [False, False, True, False]
>>> status = any(checks)
>>> status


If you ever have a loop and you also need an incrementing counter for the body of your loop, then enumerate is your friend. The function can return pairs that contain an index and the value in the list. You can also set a start keyword argument to modify the starting value of your index.

>>> fruits = ['apple', 'orange', 'kiwi', 'pear']
>>> for index, fruit in enumerate(fruits, start=1):
...     print(index, fruit)
(1, 'apple')
(2, 'orange')
(3, 'kiwi')
(4, 'pear')


The humble print statement became a print function in Python 3. There are plenty of grumpy Python 2 developers whose muscle memory prevent them from typing the function correctly (I’m often one of them), but the print function is pretty great. By making print a function instead of a keyword, developers gets all the great benefits that come from using Python functions. For example, the print function adds a lot of clarity for writing to a different file stream by using the file keyword argument rather than the odd print >> sys.stderr 'help me' style.

>>> print('Hello World')
Hello World
>>> import sys
>>> print('An error', file=sys.stderr)
An error


range is great for producing lists of values. I don’t have much to say about it. This one is fairly self-explanatory. :)

>>> range(10)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> range(5, 10)
[5, 6, 7, 8, 9]
>>> range(0, 10, 2)
[0, 2, 4, 6, 8]


Lists in Python have an included sort method. The downside of this method is that this list will be sorted in place. If you don’t like that behavior, you can get a new list by passing your original list through the sorted function. This function also has the ability to take a key function that will decide how things are sorted. Have a list of colors that you wanted sorted into a rainbow? That’s entirely possible if you’re key function knows how to sort colors that way.

>>> numbers = [5, 2, 3, 1, 4]
>>> ordered = sorted(numbers)
>>> ordered
[1, 2, 3, 4, 5]
>>> numbers
[5, 2, 3, 1, 4]
>>> numbers.sort()
>>> numbers
[1, 2, 3, 4, 5]

So much more!

Covering five example functions doesn’t even reach 10% of what Python has built in to the core. I believe your code will be way better if you can learn some of these functions and how to apply them regularly as you make new things.

Be sure to check out the docs to boost your skill set, and check back in next time when I illuminate how cool the standard library is.