Here are eight neat Python tricks some I’m sure you haven’t seen before. Apply these tricks in your Python code to make it more concise and performant!

1. Sorting Objects by Multiple Keys

Suppose we want to sort the following list of dictionaries:

people = [
{ 'name': 'John', "age": 64 },
{ 'name': 'Janet', "age": 34 },
{ 'name': 'Ed', "age": 24 },
{ 'name': 'Sara', "age": 64 },
{ 'name': 'John', "age": 32 },
{ 'name': 'Jane', "age": 34 },
{ 'name': 'John', "age": 99 },
]

But we don’t just want to sort it by name or age, we want to sort it by both fields. In SQL, this would be a query like:

SELECT * FROM people ORDER by name, age

There’s actually a very simple solution to this problem, thanks to Python’s guarantee that sort functions offer a stable sort order. This means items that compare equal retain their original order.

To achieve sorting by name and age, we can do this:

import operator
people.sort(key=operator.itemgetter('age'))
people.sort(key=operator.itemgetter('name'))

Notice how I reversed the order. We first sort by age, and then by name. With operator.itemgetter() we get the age and name fields from each dictionary inside the list in a concise way.

This gives us the result we were looking for:

[
 {'name': 'Ed',   'age': 24},
 {'name': 'Jane', 'age': 34},
 {'name': 'Janet','age': 34},
 {'name': 'John', 'age': 32},
 {'name': 'John', 'age': 64},
 {'name': 'John', 'age': 99},
 {'name': 'Sara', 'age': 64}
]

The names are sorted primarily, the ages are sorted if the name is the same. So all the Johns are grouped together, sorted by age.

2. List Comprehensions

A list comprehension can replace ugly for loops used to fill a list. The basic syntax for a list comprehension is:

[ expression for item in list if conditional ]

A very basic example to fill a list with a sequence of numbers:

mylist = [i for i in range(10)]
	print(mylist)
	# [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

And because you can use an expression, you can also do some math:

squares = [x**2 for x in range(10)]
	print(squares)
	# [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

Or even call an external function:

def some_function(a):
	    return (a + 5) / 2

	my_formula = [some_function(i) for i in range(10)]
	print(my_formula)
	# [2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0]

And finally, you can use the ‘if’ to filter the list. In this case, we only keep the values that are dividable by 2:

filtered = [i for i in range(20) if i%2==0]
	print(filtered)
	# [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

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