CODEWITHSUNDEEP
pythontuples
Ivan Novick
Ivan Novick

Reputation: 775

What makes a python tuple?

The following code does not print what I would expect:

#!/usr/bin/env python

print type(1,)
a = 1,
print type(a)

Here is the output:

<type 'int'>
<type 'tuple'>

I understand that the comma makes a into a tuple. But if that is the case how come the original print is not printing a tuple type but an int?

Upvotes: 5

Views: 368

Answers (3)

fresskoma
fresskoma

Reputation: 25781

Because the tuple syntax inside a function call is also the way parameters are passed:

>>> print type(1,2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: type() takes 1 or 3 arguments

>>> print type((1,))
<type 'tuple'>

>>> a = 1,
>>> type(a)
<type 'tuple'>

It is a syntax ambiguity for python, which it solves by deciding that you are trying to pass a parameter (if you ask me, it should be a syntax error though).

>>> print type(1,)
>>> print type(1)

Are the same.

Upvotes: 10

Martijn Pieters
Martijn Pieters

Reputation: 1121534

type() is a function, so the python parser will pass everything between the parenthesis of the type function call as the argument tuple to that function.

Thus, to pass a literal tuple to a function call you'll always need to add the parenthesis to the tuple for the parser to recognize it as such:

print type((1,))

Upvotes: 0

Alexander Gessler
Alexander Gessler

Reputation: 46607

Because it's not enclosed in parentheses: type((1,))

Without the extra parentheses it's treated as a simple parameter list in this context and the trailing semicolon is simply ignored.

Upvotes: 0

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