CODEWITHSUNDEEP
pythontuplesconcatenation
Qi Chen
Qi Chen

Reputation: 1718

Concatenate tuple with variable

I have a tuple x = (2,) to which I would like to append a variable y. I do not know ahead of time exactly what kind of variable y will be.

y could be:

Adopting one strategy will give me a TypeError half of the time, and adopting the other will give me (2, (3, 4)) when I want (2, 3, 4).

What's the best way to handle this?

Upvotes: 6

Views: 2528

Answers (2)

Luke Taylor
Luke Taylor

Reputation: 9561

Use the second strategy, just check whether you're adding an iterable with multiple items or a single item.

You can see if an object is an iterable (tuple, list, etc.) by checking for the presence of an __iter__ attribute. For example:

# Checks whether the object is iterable, like a tuple or list, but not a string.
if hasattr(y, "__iter__"):
    x += tuple(y)
# Otherwise, it must be a "single object" as you describe it.
else:
    x += (y,)

Try this. This snippet will behave exactly like you describe in your question.

Note that in Python 3, strings have an __iter__ method. In Python 2.7:

>>> hasattr("abc", "__iter__")
False

In Python 3+:

>>> hasattr("abc","__iter__")
True

If you are on Python 3, which you didn't mention in your question, replace hasattr(y, "__iter__") with hasattr(y, "__iter__") and not isinstance(y, str). This will still account for either tuples or lists.

Upvotes: 4

Bhargav Rao
Bhargav Rao

Reputation: 52071

Use isinstance in a if condition. 

>>> x = (2,)
>>> y1 = (1,2)
>>> y2 = 2
>>> def concat_tups(x,y):
...     return x + (y if isinstance(y,tuple) else (y,))
... 
>>> concat_tups(x,y2)
(2, 2)
>>> concat_tups(x,y1)
(2, 1, 2)
>>>

Upvotes: 1

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