Primary Unit

One of my favourite scripts is a snippet of Python that produces a date with an ordinal suffix. It’s short, simple, and was probably the first thing I did in Python that made me sit back and smile.

But it contains a hack to prevent the day of the month from being prefixed with a zero (%d) or a space (%e). I recently discovered that you can use a hyphen in the format specifier to prevent this: %-d.

Also, the method of inserting the suffixed day just uses str.replace to replace a hash mark. But what if you need a hash mark in your date string? Not ideal, and easily solved with Python’s str.format.

Here’s the new code:

 1from datetime import date
 2
 3def ordinal_suffix(day):
 4  if 3 < day < 21 or 23 < day < 31:
 5    return 'th'
 6  else:
 7    return {1: 'st', 2: 'nd', 3: 'rd'}[day % 10]
 8
 9today = date.today()
10date_string = today.strftime('%A, %B %-d{suffix}, %Y')
11print(date_string.format(suffix=ordinal_suffix(today.day)))

Starting with the date string on line 10, %-d surpasses the prefix, and we include a replacement field ({suffix}). That gets formatted with the output of the ordinal_suffix function.

The logic there is largely the same as before except that I’m treating the 1x numbers as a special case in line 4 (which I appreciate is a bit silly given the range 1-31, but 0x, 2x and 3x days all conform). Given a bit more thought, it makes sense to handle all th suffixes in the True part of the conditional. Everything else, as before, gets reduced to the final digit and is used to index into the dictionary in line 7 — using get to supply th as a default.

It may seem silly to revisit this — this may as well be fizzbuzz — but I really don’t like leaving blog posts that I know are incorrect in some way. I hate the idea that someone may stumble across a post and take away an idea that isn’t the best that I could provide them. And really this is a learning process for me: I think something is one way, write about it, come to a better conclusion, and write about it again.