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devel / comp.lang.python / Re: C API PyObject_CallFunctionObjArgs returns incorrect result

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o Re: C API PyObject_CallFunctionObjArgs returns incorrect resultJen Kris

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Re: C API PyObject_CallFunctionObjArgs returns incorrect result

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Subject: Re: C API PyObject_CallFunctionObjArgs returns incorrect result
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 by: Jen Kris - Mon, 7 Mar 2022 17:05 UTC

Thank you MRAB for your reply.

Regarding your first question, pSentence is a list.  In the nltk library, nltk.word_tokenize takes a string, so we convert sentence to string before we call nltk.word_tokenize:

>>> sentence = " ".join(sentence)
>>> pt = nltk.word_tokenize(sentence)
>>> print(sentence)
[ Emma by Jane Austen 1816 ]

But with the C API it looks like this:

PyObject *pSentence = PySequence_GetItem(pSents, sent_count);
PyObject* str_sentence = PyObject_Str(pSentence);  // Convert to string

; See what str_sentence looks like:
PyObject* repr_str = PyObject_Repr(str_sentence);  
PyObject* str_str = PyUnicode_AsEncodedString(repr_str, "utf-8", "~E~");  
const char *bytes_str = PyBytes_AS_STRING(str_str);
printf("REPR_String: %s\n", bytes_str); 

REPR_String: "['[', 'Emma', 'by', 'Jane', 'Austen', '1816', ']']"
So the two string representations are not the same – or at least the   PyUnicode_AsEncodedString is not the same, as each item is surrounded by single quotes. 

Assuming that the conversion to bytes object for the REPR is an accurate representation of str_sentence, it looks like I need to strip the quotes from str_sentence before “PyObject* pWTok = PyObject_CallFunctionObjArgs(pNltk_WTok, str_sentence, 0).”   

So my questions now are (1) is there a C API function that will convert a list to a string exactly the same way as ‘’.join, and if not then (2) how can I strip characters from a string object in the C API? 

Thanks.

Mar 6, 2022, 17:42 by python@mrabarnett.plus.com:

> On 2022-03-07 00:32, Jen Kris via Python-list wrote:
>
>> I am using the C API in Python 3.8 with the nltk library, and I have a problem with the return from a library call implemented with PyObject_CallFunctionObjArgs.
>>
>> This is the relevant Python code:
>>
>> import nltk
>> from nltk.corpus import gutenberg
>> fileids = gutenberg.fileids()
>> sentences = gutenberg.sents(fileids[0])
>> sentence = sentences[0]
>> sentence = " ".join(sentence)
>> pt = nltk.word_tokenize(sentence)
>>
>> I run this at the Python command prompt to show how it works:
>>
>>>>> sentence = " ".join(sentence)
>>>>> pt = nltk.word_tokenize(sentence)
>>>>> print(pt)
>>>>>
>> ['[', 'Emma', 'by', 'Jane', 'Austen', '1816', ']']
>>
>>>>> type(pt)
>>>>>
>> <class 'list'>
>>
>> This is the relevant part of the C API code:
>>
>> PyObject* str_sentence = PyObject_Str(pSentence);
>> // nltk.word_tokenize(sentence)
>> PyObject* pNltk_WTok = PyObject_GetAttrString(pModule_mstr, "word_tokenize");
>> PyObject* pWTok = PyObject_CallFunctionObjArgs(pNltk_WTok, str_sentence, 0);
>>
>> (where pModule_mstr is the nltk library).
>>
>> That should produce a list with a length of 7 that looks like it does on the command line version shown above:
>>
>> ['[', 'Emma', 'by', 'Jane', 'Austen', '1816', ']']
>>
>> But instead the C API produces a list with a length of 24, and the REPR looks like this:
>>
>> '[\'[\', "\'", \'[\', "\'", \',\', "\'Emma", "\'", \',\', "\'by", "\'", \',\', "\'Jane", "\'", \',\', "\'Austen", "\'", \',\', "\'1816", "\'", \',\', "\'", \']\', "\'", \']\']'
>>
>> I also tried this with PyObject_CallMethodObjArgs and PyObject_Call without success.
>>
>> Thanks for any help on this.
>>
> What is pSentence? Is it what you think it is?
> To me it looks like it's either the list:
>
> ['[', 'Emma', 'by', 'Jane', 'Austen', '1816', ']']
>
> or that list as a string:
>
> "['[', 'Emma', 'by', 'Jane', 'Austen', '1816', ']']"
>
> and that what you're tokenising.
> --
> https://mail.python.org/mailman/listinfo/python-list
>

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