Is it pythonic for a function to return multiple values?
In python, you can have a function return multiple values. Here's a contrived example:
def divide(x, y):
quotient = x/y
remainder = x % y
return quotient, remainder
(q, r) = divide(22, 7)
This seems very useful, but it looks like it can also be abused ("Well..function X already computes what we need as an intermediate value. Let's have X return that value also").
When should you draw the line and define a different method?
Absolutely (for the example you provided).
Tuples are first class citizens in Python
There is a builtin function divmod() that does exactly that.
q, r = divmod(x, y) # ((x - x%y)/y, x%y) Invariant: div*y + mod == x
There are other examples: zip , enumerate , dict.items .
for i, e in enumerate([1, 3, 3]):
print "index=%d, element=%s" % (i, e)
# reverse keys and values in a dictionary
d = dict((v, k) for k, v in adict.items()) # or
d = dict(zip(adict.values(), adict.keys()))
BTW, parentheses are not necessary most of the time. Citation from Python Library Reference:
Tuples are constructed by the comma operator (not within square brackets), with or without enclosing parentheses, but an empty tuple must have the enclosing parentheses, such as a, b, c or (). A single item tuple must have a trailing comma, such as (d,).
Functions should serve single purpose
Therefore they should return a single object. In your case this object is a tuple. Consider tuple as an ad-hoc compound data structure. There are languages where almost every single function returns multiple values (list in Lisp).
Sometimes it is sufficient to return (x, y) instead of Point(x, y) .
Named tuples
With the introduction of named tuples in Python 2.6 it is preferable in many cases to return named tuples instead of plain tuples.
>>> import collections
>>> Point = collections.namedtuple('Point', 'x y')
>>> x, y = Point(0, 1)
>>> p = Point(x, y)
>>> x, y, p
(0, 1, Point(x=0, y=1))
>>> p.x, p.y, p[0], p[1]
(0, 1, 0, 1)
>>> for i in p:
... print(i)
...
0
1
Firstly, note that Python allows for the following (no need for the parenthesis):
q, r = divide(22, 7)
Regarding your question, there's no hard and fast rule either way. For simple (and usually contrived) examples, it may seem that it's always possible for a given function to have a single purpose, resulting in a single value. However, when using Python for real-world applications, you quickly run into many cases where returning multiple values is necessary, and results in cleaner code.
So, I'd say do whatever makes sense, and don't try to conform to an artificial convention. Python supports multiple return values, so use it when appropriate.
The example you give is actually a python builtin function, called divmod . So someone, at some point in time, thought that it was pythonic enough to include in the core functionality.
To me, if it makes the code cleaner, it is pythonic. Compare these two code blocks:
seconds = 1234
minutes, seconds = divmod(seconds, 60)
hours, minutes = divmod(minutes, 60)
seconds = 1234
minutes = seconds / 60
seconds = seconds % 60
hours = minutes / 60
minutes = minutes % 60
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