Maltparser Giving Error in Nltk

Maltparser giving error in NLTK

The MaltParser API in NLTK just had a patch that fixes and stabilizes the problems that it used to have:

• How to use malt parser in python nltk
• Malt Parser throwing class not found exception
• MaltParser Not Working in Python NLTK

Here's an example of how to use MaltParser API in NLTK:

# Upgrade your NLTK.
alvas@ubi:~$ cd ~
alvas@ubi:~$ pip install -U nltk

# Get the latest MaltParser and model
alvas@ubi:~$ wget http://maltparser.org/dist/maltparser-1.8.1.zip
alvas@ubi:~$ unzip maltparser-1.8.1.zip 
alvas@ubi:~$ wget http://www.maltparser.org/mco/english_parser/engmalt.poly-1.7.mco

# In python, now you can do this:
alvas@ubi:~$ python
>>> from nltk.parse.malt import MaltParser
>>> mp = MaltParser('/home/alvas/maltparser-1.8.1', '/home/alvas/engmalt.poly-1.7.mco')
>>> sent1 = 'I shot an elephant in my pajamas .'.split()
>>> print(mp.parse_one(sent1).tree())
(shot I (elephant an (in (pajamas my))) .)

(See here for more demo code or here for a more elaborated demo code)

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Note that you can also use the export features and you can escape the usage of full path when initializing the MaltParser object. But you have to still tell the object what is the name of the parser directory and model filename to look for, e.g.

alvas@ubi:~$ export MALT_PARSER='/home/$UID/maltparser-1.8.1/'
alvas@ubi:~$ export MALT_MODEL='/home/$UID/engmalt.poly-1.7.mco' 
alvas@ubi:~$ python
>>> from nltk.parse.malt import MaltParser
>>> mp = MaltParser('maltparser-1.8.1', 'engmalt.poly-1.7.mco')
>>> sent1 = 'I shot an elephant in my pajamas .'.split()
>>> print(mp.parse_one(sent1).tree())
(shot I (elephant an (in (pajamas my))) .)

NLTK MaltParser won't parse

Iam not sure if the Problem is still unsolved (but I think its already solved),
but as I had the same problems a while ago, I would like to share my knowledge.

First of all, the MaltParser-Jar does not accept a .connl file with a direct path to its file in front of it. Like seen above.
Why it is so... I do not know.

But you can easily fix it by changing the command line to something like this:

            cmd = ['java', '-jar %s' % self._malt_bin,'-w %s' %self.working_dir,'-c %s' % self.mco, '-i %s' % input_file, '-o %s' % output_file, '-m parse']

Here now the directory of the .conll file is set using the -w parameter. Using this you can load any .conll file from any given folder.
I also change from tempfile.gettempdir() to self.working_dir, because in the "original" NLTK Version, always the /tmp/ folder is set as working directory. Even if you initialise the Maltparser with another working directory.

I hope this informations will help someone.

Another thing,
if you want to parse many sentences as once, but each individually and not depending on all other sentences, you have to add a blank line in the input.conll file, and start the numeration for each sentence again with 1.

How to use malt parser in python nltk

Edited

Note that is answer is no longer working because of the updated version of the MaltParser API in NLTK since August 2015. This answer is kept for legacy sake.

Please see this answers to get MaltParser working with NLTK:

• Step by step to getting malt parser in NLTK to work?

Disclaimer: This is not an eternal solutions. The answer in the above link (posted on Feb 2016) will work for now. But when MaltParser or NLTK API changes, it might also change the syntax to using MaltParser in NLTK.

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A couple problems with your setup:

• The input to train_from_file must be a file in CoNLL format, not a pre-trained model. For an mco file, you pass it to the MaltParser constructor using the mco and working_directory parameters.
• The default java heap allocation is not large enough to load that particular mco file, so you'll have to tell java to use more heap space with the -Xmx parameter. Unfortunately this wasn't possible with the existing code so I just checked in a change to allow an additional constructor parameters for java args. See here.

So here's what you need to do:

First, get the latest NLTK revision:

git clone https://github.com/nltk/nltk.git

(NOTE: If you can't use the git version of NLTK, then you'll have to update the file malt.py manually or copy it from here to have your own version.)

Second, rename the jar file to malt.jar, which is what NLTK expects:

cd /usr/lib/
ln -s maltparser-1.7.2.jar malt.jar

Then add an environment variable pointing to malt parser:

export MALTPARSERHOME="/Users/dhg/Downloads/maltparser-1.7.2"

Finally, load and use malt parser in python:

>>> import nltk
>>> parser = nltk.parse.malt.MaltParser(working_dir="/home/rohith/malt-1.7.2", 
...                                     mco="engmalt.linear-1.7", 
...                                     additional_java_args=['-Xmx512m'])
>>> txt = "This is a test sentence"
>>> graph = parser.raw_parse(txt)
>>> graph.tree().pprint()
'(This (sentence is a test))'

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