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Python Decorators: What they are underneath

22 points by dhotson 18y ago

mk 18y ago
The article that this article is responding to is useful in understanding as well. http://sgillies.net/blog/858/how-to-decorate-python-gis-code/ http://sgillies.net/blog/858/how-to-decorate-python-gis-code... This one as well. http://www.artima.com/weblogs/viewpost.jsp?thread=240845 http://www.artima.com/weblogs/viewpost.jsp?thread=240845
jamongkad 18y ago
Thank you! I've been trying to wrap my head around decorators this past week. Definitely a good guide.
- kaens 18y ago
  Really, the only thing you need to wrap your head around to understand decorators is the concept of first-class functions (functions that can take functions as parameters and return functions). If you understand those, and how they can be useful, the only remaining step to python's decorators is a syntactic transformation. def decorate(func): def wrapper(*args, **kwargs): print "I'm decorated!" return func(*args, **kwargs) return wrapper @decorate def foo(): print "I'm foo!" Above, @decorate is equivalent to having foo = decorate(foo) underneath the definition of foo. Decorate takes a function X as a parameter, creates a function Y that takes whatever arguments, prints a statement, and returns the value of calling Y with whatever arguments. It then returns the object representing X. If you need a bunch of good examples of how first-class functions can be extremely useful, go through a bit of SICP ( http://mitpress.mit.edu/sicp/full-text/book/book.html http://mitpress.mit.edu/sicp/full-text/book/book.html ). It's a challenging tome, but well worth the effort.
cgranade 18y ago
I didn't realize that Jython was out-of-date enough to miss decorators... I hope that Jython doesn't die.
- jdunck 18y ago
  "As of October 31, 2008, the Jython development team is proud to announce a new beta release: Jython 2.5b0!" http://www.jython.org/Project/ http://www.jython.org/Project/ Jython is alive and well.

22 points by dhotson 18y ago

mk 18y ago

The article that this article is responding to is useful in understanding as well. http://sgillies.net/blog/858/how-to-decorate-python-gis-code/ http://sgillies.net/blog/858/how-to-decorate-python-gis-code... This one as well. http://www.artima.com/weblogs/viewpost.jsp?thread=240845 http://www.artima.com/weblogs/viewpost.jsp?thread=240845

jamongkad 18y ago

Thank you! I've been trying to wrap my head around decorators this past week. Definitely a good guide.

kaens 18y ago
Really, the only thing you need to wrap your head around to understand decorators is the concept of first-class functions (functions that can take functions as parameters and return functions). If you understand those, and how they can be useful, the only remaining step to python's decorators is a syntactic transformation. def decorate(func): def wrapper(*args, **kwargs): print "I'm decorated!" return func(*args, **kwargs) return wrapper @decorate def foo(): print "I'm foo!" Above, @decorate is equivalent to having foo = decorate(foo) underneath the definition of foo. Decorate takes a function X as a parameter, creates a function Y that takes whatever arguments, prints a statement, and returns the value of calling Y with whatever arguments. It then returns the object representing X. If you need a bunch of good examples of how first-class functions can be extremely useful, go through a bit of SICP ( http://mitpress.mit.edu/sicp/full-text/book/book.html http://mitpress.mit.edu/sicp/full-text/book/book.html ). It's a challenging tome, but well worth the effort.

cgranade 18y ago

I didn't realize that Jython was out-of-date enough to miss decorators... I hope that Jython doesn't die.

jdunck 18y ago
"As of October 31, 2008, the Jython development team is proud to announce a new beta release: Jython 2.5b0!" http://www.jython.org/Project/ http://www.jython.org/Project/ Jython is alive and well.