Getting Started with Sorting in Python

2020-12-05

Intro

Python has two built in sort functions: sort and sorted. The sort function will modify the list and sort it in-place. Sorted will take a list and return a new list sorted.

Why have two methods? Well, it is a somewhat more advance topic, but both have design advantages. Sometimes you want to sort in-plae to save memory. Othere times, you don't care about memory as much and want to return a new list to keep immutability. We will cover these ideas in the future if you haven't heard of them.

The .sort function

We begin with an example of the .sort function. This is a method attached to the stardard list. Here is how we can sort a list of numbers.

arr = [5, 6, 1, 3]
arr.sort()

print(arr)

And if we wish to reverse the order (sort descending), we pass the reverse option.

arr = [5, 6, 1, 3]
arr.sort(reverse=True)

print(arr)

We can also get a little advanced. Let's say we want to sort a list of dictionaries by a property. We can pass a lambda (think of it as passing a function) to the sort method's key parameter. Below says to sort the dictionaries by the str key.

stats = [
  {'hero': 'John Doe', 'str': 19, 'mp': 43},
  {'hero': 'Robert Smith', 'str': 49, 'mp': 43},
  {'hero': 'Dean Brown', 'str': 34, 'mp', 45},
]

stats.sort(key=lambda item: item['str'])

The sorted function

Now, for the sorted function, everything works the same way, but instead of calling a method on a list, we use a build in python function.

arr = [5, 6, 1, 3]
newArr = sorted(arr)

print(newArr)
arr = [5, 6, 1, 3]
newArr = sorted(arr, reverse=True)

print(newArr)
stats = [
  {'hero': 'John Doe', 'str': 19, 'mp': 43},
  {'hero': 'Robert Smith', 'str': 49, 'mp': 43},
  {'hero': 'Dean Brown', 'str': 34, 'mp', 45},
]

newArr = sorted(users, key=lambda e: e['name'])
print(newArr)

Conclusion

The sort methods for python are very pthon. The ability to have a custom sort allows us to sort many different objects. Check out the docs for more info: https://docs.python.org/3/howto/sorting.html.

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