python2 lambda syntax error with three-tuple argument in python3

Asked May 28 '20 at 09:24

Active May 28 '20 at 09:38

Viewed 37 times

I'm getting a SyntaxError using a lambda with a three-tuple

candidates = [' '.join(word for word, pos, chunk in group).lower()
              for key, group in itertools.groupby(all_chunks, lambda (word,pos,chunk): chunk != 'O') if key]

where all_chunks is a list.

the error is

 for key, group in itertools.groupby(all_chunks, lambda (word,pos,chunk): chunk != 'O') if key]
                                                           ^
SyntaxError: invalid syntax

That syntax is valid in Python2, but not in Python3. The tuple is a three-tuple, otherwise getting a TypeError error

     13     # join constituent chunk words into a single chunked phrase
---> 14     candidates = [' '.join(word for word, pos, chunk in group).lower()
     15                   for key, group in itertools.groupby(all_chunks, lambda word,pos,chunk: chunk != 'O') if key]
     16 

TypeError: <lambda>() missing 2 required positional arguments: 'pos' and 'chunk'

edited May 28 '20 at 09:38

asked May 28 '20 at 09:24

loretoparisi

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Try `lambda woPoCh: woPoCh[2] != 'O')` . Also know that you need to sort `all_chunk` but the SAME KEY you use for the groupby or it won't work – azro May 28 '20 at 09:26
this is one of my least favourite things about python 3, this worked in python 2 – Chris_Rands May 28 '20 at 09:28
@azro I think now this is related to Python2 / Python3. To syntax is ok in Python2, not in Python3. Why? – loretoparisi May 28 '20 at 09:30
1

Because python3 is not python2, theyr changed that's it – azro May 28 '20 at 09:30
yes just updated the question to be more specific about the right python3 syntax. – loretoparisi May 28 '20 at 09:32
According to the language's [grammer](https://docs.python.org/3/reference/expressions.html#lambda) the same rules as function definitions apply to lambdas. So it is just like you will not do `def foo(a, (b,c), d):`. Either take 3 arguments, or one argument and unpack it inside the lambda – Tomerikoo May 28 '20 at 09:35
What is `group` ? – May 28 '20 at 09:36
@Tomerikoo okay so this syntax was still valid in Python2 and changed in Python3? – loretoparisi May 28 '20 at 09:36
1

Apparently... @nakE it is the value returned by `groupby` – Tomerikoo May 28 '20 at 09:37
1

Note: https://www.python.org/dev/peps/pep-3113/ – juanpa.arrivillaga May 28 '20 at 09:42
@juanpa.arrivillaga could it be still possible to unpack using the `*` splash as `Extended Iterable Unpacking`? https://www.python.org/dev/peps/pep-3132/ – loretoparisi May 28 '20 at 09:53
1

@loretoparisi sure, but not in the parameters, and that would have to be a statement, which can't be part of a lambda – juanpa.arrivillaga May 28 '20 at 10:24
@juanpa.arrivillaga ok thanks how to apply in this case? I'm not sure if I must explicitly expand all the for loop here and use a named function instead of a lambda then... – loretoparisi May 28 '20 at 10:27
1

Well, you an just use `lambda triple: triple[2] != '0'` – juanpa.arrivillaga May 28 '20 at 10:37
@juanpa.arrivillaga right, there's no need to expand the tuple actually! Please answer so I can accept. – loretoparisi May 28 '20 at 10:48

python2 lambda syntax error with three-tuple argument in python3

0 Answers0