Python lambda does not accept tuple argument [duplicate]

Question

I am running Eclipse SDK v3.6 with PyDev v2.6 plugin on two PC, with Linux and Windows.

I would like to pass a tuple as an argument, like:

foo = lambda (x,y): (y,x)
print (foo((1,2)))

This works on Linux and gives the correct result:

> (2,1)

On Windows it rises an error:

foo = lambda (x,y): (y,x)
             ^
SyntaxError: invalid syntax

How to solve the problem?

Answer 1

You are probably running Python 3.x on Windows, and Python 2.x on Linux. The ability to unpack tuple parameters was removed in Python 3: See PEP 3113.

You can manually unpack the tuple instead, which would work on both Python 2.x and 3.x:

foo = lambda xy: (xy[1],xy[0])

Or:

def foo(xy):
    x,y = xy
    return (y,x)