Python dictionary comprehensions

Python programmers may be familiar with list comprehensions, a compact syntax for defining a list. Here's a typical example that creates a list containing the squares of the first five positive integers:

print [n*n for n in range(1,6)]
[1, 4, 9, 16, 25]

But suppose we want to create a dictionary, rather than just a list, mapping each integer to its square. We can use a dictionary comprehension. It differs from a list comprehension in using curly braces instead of square brackets, and in specifying two expressions separated by a colon to the left of the

for.

print {n: n*n for n in range(1,6)}
{1: 1, 2: 4, 3: 9, 4: 16, 5: 25}

This is equivalent to:

d = {}
for n in range(1,6):
    d[n] = n*n
print d

Dictionary comprehensions are a great of example of how we can do a lot in Python with a single, very readable, line of code.