{"id":567,"date":"2017-07-22T09:13:44","date_gmt":"2017-07-22T09:13:44","guid":{"rendered":"http:\/\/www.rangakrish.com\/?p=567"},"modified":"2017-07-22T09:18:36","modified_gmt":"2017-07-22T09:18:36","slug":"clpython-python-in-common-lisp-part-2","status":"publish","type":"post","link":"https:\/\/www.rangakrish.com\/index.php\/2017\/07\/22\/clpython-python-in-common-lisp-part-2\/","title":{"rendered":"CLPython: Python in Common Lisp – Part 2"},"content":{"rendered":"

We looked at the basic features of CLPython<\/a>\u00a0in our last blog<\/a>. In today’s post let us look at the support for Python classes.<\/p>\n

PYTEST 130 > (defun pyclass ()<\/span><\/strong><\/p>\n

\u00a0 (run\u00a0<\/span><\/strong><\/p>\n

“class Employee:<\/span><\/strong><\/p>\n

\u00a0\u00a0 def __init__(self, name, dept):<\/span><\/strong><\/p>\n

\u00a0\u00a0 \u00a0 self.name = name<\/span><\/strong><\/p>\n

\u00a0\u00a0 \u00a0 self.dept = dept<\/span><\/strong><\/p>\n

\u00a0\u00a0 def dump(self):<\/span><\/strong><\/p>\n

\u00a0\u00a0 \u00a0 print ‘Name = ‘, self.name, ‘, Dept = ‘, self.dept<\/span><\/strong><\/p>\n

\u00a0\u00a0 def setDept(self, dept):<\/span><\/strong><\/p>\n

\u00a0\u00a0 \u00a0 self.dept = dept<\/span><\/strong><\/p>\n

“))<\/span><\/strong><\/p>\n

PYCLASS<\/span><\/strong><\/p>\n

PYTEST 131 > (setf cls (pyclass))<\/span><\/strong><\/p>\n

#<class Employee 40202F63AB><\/span><\/strong><\/p>\n

We have now defined a Python class (called Employee<\/strong><\/em>) on the fly. The variable cls<\/strong><\/em> stores the Lisp representation of the class.<\/p>\n

One way to create an instance of this class is execute a corresponding Python command in Lisp:<\/p>\n

PYTEST 132 > (setf obj (run “x = Employee(‘John’, ‘Sales’)”))<\/strong><\/span><\/p>\n

#<Employee 402008052B><\/strong><\/span><\/p>\n

As you can guess, x<\/strong><\/em> is a Python variable and obj<\/strong><\/em> is a Lisp variable, both referencing\u00a0the same Employee<\/strong><\/em> object. Another way is to create the instance directly in Lisp using the CLPython function py-call<\/strong><\/em>:<\/p>\n

PYTEST 133 > (setf obj2 (py-call cls “Mary” “HR”))<\/strong><\/span><\/p>\n

#<Employee 40200932F3><\/strong><\/span><\/p>\n

Note that in both cases, we have to supply the constructor arguments.<\/p>\n

We can invoke the dump<\/strong><\/em> method and see the the values of the instance varables:<\/p>\n

PYTEST 134 > (run “x.dump()”)<\/strong><\/span><\/p>\n

Name =\u00a0 John , Dept =\u00a0 Sales<\/strong><\/span><\/p>\n

None<\/strong><\/span><\/p>\n

What about accessing the methods through the Lisp object? Unfortunately, I could not find a way to do this.<\/p>\n

The documentation says that Python class is mapped to CLOS class and instance is mapped to CLOS instance. So I decided to introspect the class\/object using methods in the CLOS Meta Object Protocol (MOP).<\/p>\n

PYTEST 135 > (class-slots cls)<\/strong><\/span><\/p>\n

(#<STANDARD-EFFECTIVE-SLOT-DEFINITION CLPYTHON::DICT 4020155263>)<\/strong><\/span><\/p>\n

PYTEST 136 > (mapcar #’slot-definition-name (class-slots cls))<\/strong><\/span><\/p>\n

(CLPYTHON::DICT)<\/strong><\/span><\/p>\n

It appears as if there is just one slot called DICT<\/strong><\/em> in the corresponding Lisp class. We can retrieve its values thus:<\/p>\n

PYTEST 137 > (slot-value obj ‘CLPYTHON::dict)<\/strong><\/span><\/p>\n

((CLPYTHON.USER::|dept| . “Sales”) (CLPYTHON.USER::|name| . “John”))<\/strong><\/span><\/p>\n

So the various instance variables and values are stored as cons pairs<\/strong><\/em> in this single slot.<\/p>\n

OK, can we change the vaue of the field directly via the slot?<\/p>\n

PYTEST 138 > (setf (first (slot-value obj ‘CLPYTHON::dict)) ‘(CLPYTHON.USER::|dept| . “PR”))<\/strong><\/span><\/p>\n

(CLPYTHON.USER::|dept| . “PR”)<\/strong><\/span><\/p>\n

PYTEST 139 > (run “x.dump()”)<\/strong><\/span><\/p>\n

Name =\u00a0 John , Dept =\u00a0 PR<\/strong><\/span><\/p>\n

None<\/strong><\/span><\/p>\n

OK, that is nice!<\/p>\n

We can change the dept<\/strong><\/em> by invoking the instance method as well:<\/p>\n

PYTEST 140\u00a0> (run “x.setDept(‘Mktg’)”)<\/strong><\/span><\/p>\n

None<\/strong><\/span><\/p>\n

PYTEST 141\u00a0> (run “x.dump()”)<\/strong><\/span><\/p>\n

Name =\u00a0 John , Dept =\u00a0 Mktg<\/strong><\/span><\/p>\n

None<\/strong><\/span><\/p>\n

This is confirmed via the other Lispy check:<\/p>\n

PYTEST 142\u00a0> (slot-value obj ‘CLPYTHON::dict)<\/strong><\/span><\/p>\n

((CLPYTHON.USER::|dept| . “Mktg”) (CLPYTHON.USER::|name| . “John”))<\/strong><\/span><\/p>\n

One thing that is apparent from my investigation is that the mapping from Python class to Lisp class is not exact. What I mean is that Python class is not mapped to Lisp class with the fields being mapped to slots<\/strong><\/em> and methods to defmethods<\/strong><\/em>. Maybe there was a reason to do it this way. That is perfectly understandable.<\/p>\n

Well, that concludes my brief study of CLPython. Have a great day!<\/p>\n","protected":false},"excerpt":{"rendered":"

We looked at the basic features of CLPython\u00a0in our last blog. In today’s post let us look at the support for Python classes. PYTEST 130 > (defun pyclass () \u00a0 (run\u00a0 “class Employee: \u00a0\u00a0 def __init__(self, name, dept): \u00a0\u00a0 \u00a0 self.name = name \u00a0\u00a0 \u00a0 self.dept = dept \u00a0\u00a0 def dump(self): \u00a0\u00a0 \u00a0 print ‘Name […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"advanced_seo_description":"","jetpack_seo_html_title":"","jetpack_seo_noindex":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[18,17,103],"tags":[104,19,105,106],"class_list":["post-567","post","type-post","status-publish","format-standard","hentry","category-lisp","category-programming","category-python","tag-clpython","tag-lisp","tag-meta-object-protocol","tag-mop"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p9OLnF-99","jetpack-related-posts":[{"id":558,"url":"https:\/\/www.rangakrish.com\/index.php\/2017\/07\/07\/clpython-python-in-common-lisp\/","url_meta":{"origin":567,"position":0},"title":"CLPython – Python in Common Lisp","author":"admin","date":"July 7, 2017","format":false,"excerpt":"My work in the area of NLP requires\u00a0me to work with several frameworks across multiple languages such as Java, Python and Lisp. 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