Lambda sort in Python 3

Question

I'm trying to convert code from Python 2.x to 3.x from here as and have stumbled over a syntax error with Lambda.

colours.sort(key=lambda (r,g,b): step(r,g,b,8)) # invalid syntax

I assumed that the parentheses before the colon are not needed

colours.sort(key=lambda r,g,b: step(r,g,b,8))

Only that results in a TypeError: () missing 2 required positional arguments: 'g' and 'b'

Can anyone point out where I'm going wrong?

AKX · Accepted Answer · 2020-10-11 14:01:28Z

2

Tuple unpacking in lambda arguments was removed in Python 3.

You'll need to manually index into the tuple.

colours.sort(key=lambda rgb: step(rgb[0],rgb[1],rgb[2],8))

answered Oct 11, 2020 at 14:01

AKX

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1 Comment

Yes. That makes sense now. Thank you.