Python Cookbook

Constructing a Dictionary Without Excessive Quoting

Credit: Brent Burley

Problem

You’d like to construct a dictionary without having to quote the keys.

Solution

Once you get into the swing of Python, you may find yourself constructing a lot of dictionaries. However, the standard way, also known as a dictionary display, is just a smidgeon more cluttered than you might like, due to the need to quote the keys. For example:

data = { 'red' : 1, 'green' : 2, 'blue' : 3 }

When the keys are identifiers, there’s a cleaner way:

def makedict(**kwargs):
    return kwargs
data = makedict(red=1, green=2, blue=3)

You might also choose to forego some simplicity to gain more power. For example:

def dodict(*args, **kwds):
    d = {}
    for k, v in args: d[k] = v
    d.update(kwds)
    return d
tada = dodict(yellow=2, green=4, *data.items())

Discussion

The syntax for constructing a dictionary can be slightly tedious, due to the amount of quoting required. This recipe presents a technique that avoids having to quote the keys, when they are identifiers that you already know at the time you write the code.

I’ve often found myself missing Perl’s => operator, which is well suited to building hashes (Perl-speak for dictionaries) from a literal list:

%data = (red => 1, green => 2, blue => 3);

The => operator in Perl is equivalent to Perl’s own ,, except that it implicitly quotes the word to its left.

Perl’s syntax is very similar to Python’s function-calling syntax for passing keyword arguments. And the fact that Python collects the ...