The method of insert doesn't work with nltk texts: AttributeError: 'ConcatenatedCorpusView' object has no attribute 'insert'

[Peter Otten]

Token Type wrote:

> I wrote codes to add 'like' at the end of every 3 word in a nltk text as 
follows:
> 
> >>> text = nltk.corpus.brown.words(categories = 'news')
> >>> def hedge(text):
>         for i in range(3,len(text),4):
>                 new_text = text.insert(i, 'like')
>         return new_text[:50]
> 
> >>> hedge(text)
> 
> Traceback (most recent call last):
>   File "<pyshell#77>", line 1, in <module>
>     hedge(text)
>   File "<pyshell#76>", line 3, in hedge
>     new_text = text.insert(i, 'like')
> AttributeError: 'ConcatenatedCorpusView' object has no attribute 'insert'
> 
> Isn't text in the brown corpus above a list? why doesn't it has attribute 
'insert'?
> 
> Thanks much for your hints.

The error message shows that text is not a list. It looks like a list,

>>> text = nltk.corpus.brown.words(categories="news")
>>> text
['The', 'Fulton', 'County', 'Grand', 'Jury', 'said', ...]

but it is actually a nltk.corpus.reader.util.ConcatenatedCorpusView:

>>> type(text)
<class 'nltk.corpus.reader.util.ConcatenatedCorpusView'>

The implementer of a class is free to decide what methods he wants to 
implement. You can get a first impression of the available ones with dir():

>>> dir(text)
['_MAX_REPR_SIZE', '__add__', '__class__', '__cmp__', '__contains__', 
'__delattr__', '__dict__', '__doc__', '__format__', '__getattribute__', 
'__getitem__', '__hash__', '__init__', '__iter__', '__len__', '__module__', 
'__mul__', '__new__', '__radd__', '__reduce__', '__reduce_ex__', '__repr__', 
'__rmul__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 
'__weakref__', '_offsets', '_open_piece', '_pieces', 'close', 'count', 
'index', 'iterate_from']

As you can see insert() is not among these methods. However, __iter__() is a 
hint that you can convert the ConcatenatedCorpusView to a list, and that 
does provide an insert() method. Let's try:

>>> text = list(text)
>>> type(text)
<type 'list'>
>>> text.insert(0, "yadda")
>>> text[:5]
['yadda', 'The', 'Fulton', 'County', 'Grand']

Note that your hedge() function may still not work as you expect:

>>> text = ["-"] * 20
>>> text
['-', '-', '-', '-', '-', '-', '-', '-', '-', '-', '-', '-', '-', '-', '-', 
'-', '-', '-', '-', '-']
>>> for i in range(0, len(text), 3):
...     text.insert(i, "X")
... 
>>> text
['X', '-', '-', 'X', '-', '-', 'X', '-', '-', 'X', '-', '-', 'X', '-', '-', 
'X', '-', '-', 'X', '-', '-', '-', '-', '-', '-', '-', '-']

That is because the list is growing with every insert() call. One workaround 
is to start inserting items at the end of the list:
>>> text = ["-"] * 20
>>> for i in reversed(range(0, len(text), 3)):
...     text.insert(i, "X")
... 
>>> text
['X', '-', '-', '-', 'X', '-', '-', '-', 'X', '-', '-', '-', 'X', '-', '-', 
'-', 'X', '-', '-', '-', 'X', '-', '-', '-', 'X', '-', '-']