Pythonic way of adding "ly" to end of string if it ends in "ing"?

Question

This is my first effort on solving the exercise. I gotta say, I'm kind of liking Python. :D

# D. verbing
# Given a string, if its length is at least 3,
# add 'ing' to its end.
# Unless it already ends in 'ing', in which case
# add 'ly' instead.
# If the string length is less than 3, leave it unchanged.
# Return the resulting string.
def verbing(s):
  if len(s) >= 3:
    if s[-3:] == "ing":
      s += "ly"
    else:
      s += "ing"
    return s
  else:
    return s 

  # +++your code here+++
  return

What do you think I could improve on here?

Answer 1

Pretty good for a beginner! Yes, I would say this is the Pythonic way of doing things. I especially like the way you have commented exactly what the function does. Good work there.

Keep working with Python, though. You're doing fine.

Answer 2

def verbing(s):
  if len(s) >= 3:
    if s.endswith("ing"):
      s += "ly"
    else:
      s += "ing"
  return s

Answer 3

How about this little rewrite:

def verbing(s):
    if len(s) < 3:
        return s
    elif s.endswith('ing'):
        return s + 'ly'
    else:
        return s + 'ing'

Answer 4

I would use s.endswith("ing") in the if, which is also a bit faster, because it doesn't create a new string for the comparision.

And second, I would use docstrings for commenting. This way, you can see your description when you do a help(yourmodule) or when you use some autodoc-tool like Sphinx to create a handbook describing your API. Example:

def verbings(s):
    """Given a string, if its length is at least 3, add 'ing' to its end.
    Unless it already ends in 'ing', in which case add 'ly' instead.
    If the string length is less than 3, leave it unchanged."""
    # rest of the function

Third, it's often considered a bad practice to change input parameters. You can do it for dict or list parameters, which can also act as output parameters. But strings are input parameters only (that's why you have the return). The source you have written is valid of course, but is often confusing. Other languages have often a final or const keyword to avoid this confusion, but Python doesn't. So, I would recommend you, to use either a second variable result = s + "ing" and do a return result afterwards, or write return s + "ing".

The rest is perfectly fine. There are of course some constructs in Python which are shorter to write (you will learn them with the time), but they are often not so readable. Therefore I would stay with your solution.