what is meaning of "@" in pyhon program.

[Evan]

HI,

When I check example of "cmd2" module (a enhancement of cmd module), I
can not understand all, for example: the character "@",

+++++++++++++++++++++++++++++++++++++++++++++++++++++
def options(option_list):
..........<function content>........

class cmd(...):
...............................
@options([make_option('-p', '--piglatin', action="store_true",
help="atinLay")])
+++++++++++++++++++++++++++++++++++++++++++++++++++++

I do not understand what "@options" does, most time, I know what the
meaning of character "*" and character "**", but I was not use "@"
before.

Thanks for your help.

 

[Mike Driscoll]

HI,

When I check example of "cmd2" module (a enhancement of cmd module), I
can not understand all, for example: the  character "@",

+++++++++++++++++++++++++++++++++++++++++++++++++++++
def options(option_list):
     ..........<function content>........

class cmd(...):
    ...............................
    @options([make_option('-p', '--piglatin', action="store_true",
help="atinLay")])
+++++++++++++++++++++++++++++++++++++++++++++++++++++

I do not understand what "@options" does,   most time, I know what the
meaning of character "*" and character "**", but I was not use "@"
before.

Thanks for your help.

The "@" sign is there to signify that what follows is a decorator.
They're kind of cool and kind of confusing. Basically they dynamically
alter a function, method or class and gives them additional
functionality. It's kind of like calling a function recursively. Check
out the following links:

http://www.python.org/dev/peps/pep-0318/
http://wiki.python.org/moin/PythonDecorators
http://www.ibm.com/developerworks/linux/library/l-cpdecor.html

Mike

 

[Evan]

cool, thanks, I will check document.

 

[Bruno Desthuilliers]

Mike Driscoll a écrit :

HI,

When I check example of "cmd2" module (a enhancement of cmd module), I
can not understand all, for example: the character "@",

+++++++++++++++++++++++++++++++++++++++++++++++++++++
def options(option_list):
..........<function content>........

class cmd(...):
...............................
@options([make_option('-p', '--piglatin', action="store_true",
help="atinLay")])
+++++++++++++++++++++++++++++++++++++++++++++++++++++

I do not understand what "@options" does, most time, I know what the
meaning of character "*" and character "**", but I was not use "@"
before.

Thanks for your help.

The "@" sign is there to signify that what follows is a decorator.
They're kind of cool and kind of confusing. Basically they dynamically
alter a function, method or class and gives them additional
functionality. It's kind of like calling a function recursively.

Mostly, it's just syntactic sugar for an higher order function. IOW, given:

def deco(func):
# do anythin you wish here
# and return any callable object
return any_callable_object

the two following syntaxes are equivalent:

def toto():
pass
toto = deco(toto)

@deco
def toto():
pass

 

[Damon Getsman]

Okay, maybe I just didn't understand the websites that were given as
examples as to 'decoration'. I first came across the unusual '@' when
I was browsing through some extreme beginner's information on os.x
method descriptions. I asked some other people about it and they had
no idea what it meant. I don't _THINK_ that the decoration definition
fits, though, because the examples that I saw it in had it prefixing
an if conditional & a for loop.

ie:
@if os.exists(foo):
etc
etc

and

@for blah:
etc
etc

does this mean that the person writing the script defined a function
instead of the standard conditional and loop? I can't imagine that
would be the case because, as I said, this was very beginning level
documentation.

-Damon Getsman

 

[Bruno Desthuilliers]

Damon Getsman a écrit :

Okay, maybe I just didn't understand the websites that were given as
examples as to 'decoration'. I first came across the unusual '@' when
I was browsing through some extreme beginner's information on os.x
method descriptions. I asked some other people about it and they had
no idea what it meant. I don't _THINK_ that the decoration definition
fits, though, because the examples that I saw it in had it prefixing
an if conditional & a for loop.

ie:
@if os.exists(foo):
etc
etc

and

@for blah:
etc
etc

This is not valid Python. period.

 

[John Salerno]

Okay, maybe I just didn't understand the websites that were given as
examples as to 'decoration'. I first came across the unusual '@' when
I was browsing through some extreme beginner's information on os.x
method descriptions. I asked some other people about it and they had
no idea what it meant. I don't _THINK_ that the decoration definition
fits, though, because the examples that I saw it in had it prefixing
an if conditional & a for loop.

The OP's code sample makes sense for decorators, I think. Can you post an
actual sample of what it is you saw? Sounds weird.

 

[Damon Getsman]

I didn't think that it was. I just spent about 10 minutes trying to
google for the page that I found that on, but I wasn't able to turn it
up. My google-fu sucks. I know that I was researching a particular
part of the os module and that the snippets of script on the page had
an example containing '@if' and '@for'. I don't remember what exactly
I used to turn it up before, though, and the link isn't in my history,
it was probably a month ago that I saw it.

Sorry, I tried.

 

[Aahz]

Okay, maybe I just didn't understand the websites that were given as
examples as to 'decoration'. I first came across the unusual '@' when
I was browsing through some extreme beginner's information on os.x
method descriptions. I asked some other people about it and they had
no idea what it meant. I don't _THINK_ that the decoration definition
fits, though, because the examples that I saw it in had it prefixing
an if conditional & a for loop.

ie:
@if os.exists(foo):
etc
etc

and

@for blah:
etc
etc

Guessing:

This is either a source document of text where "@" is some kind of markup
indicating a keyword (so that keywords can be e.g. bolded in the output)
or this is a snippet of code from some kind of Python-based HTML
templating language where "@" is used to indicate Python keywords that
need to be interpreted instead of static text.

 

[Thierry]

ie:

@if os.exists(foo):
   etc
   etc

and

@for blah:
   etc
   etc

This sounds more like PHP code, where a @ prefixing a function means
that even if there are errors or warnings, you don't want to see them.

 

[cokofreedom]

This sounds more like PHP code, where a @ prefixing a function means
that even if there are errors or warnings, you don't want to see them.

Could also by Doxygen, doesn't it use something similar to show
keywords in documents?