Re: Newbie: How can I use a string value for a keyword argument?
- From: Doug Morse <morse@xxxxxxxxx>
- Date: Mon, 25 Feb 2008 12:41:59 +0000 (UTC)
On Mon, 25 Feb 2008 04:20:37 -0800 (PST), John Machin <sjmachin@xxxxxxxxxxx>
wrote:
On Feb 25, 10:42 pm, Doug Morse <mo...@xxxxxxxxx> wrote:
Hi,
My apologies for troubling for what is probably an easy question... it's just
that can't seem to find an answer to this anywhere (Googling, pydocs, etc.)...
I have a class method, MyClass.foo(), that takes keyword arguments. For
example, I can say:
x = MyClass()
x.foo(trials=32)
Works just fine.
What I need to be able to do is call foo() with a string value specifying the
keyword (or both the keyword and value would be fine), something along the
lines of:
x = MyClass()
y = 'trials=32'
x.foo(y) # doesn't work
or
x.MyClass()
y = 'trials'
x.foo(y = 32) # does the "wrong" thing
Surely there's some way to use a string's value as the key for making a method
call with a keyword argument?
Just for completeness, my goal is simply to read a bunch of key/value pairs
from an INI file (using ConfigObj) and then use those key/value pairs to set a
(3rd party) object's parameters, which must be done with a call along the
lines of "instance.set(key=value)". Obviously, I could create a huge if..elif
statement along the lines of "if y = 'trials': x.foo(trials=32); elif y =
'speed': x.foo(speed=12);" etc., but then the statement has to be maintained
every time a new parameter is added/changed etc. Plus, such a solution seems
to me grossly inelegant and un-Pythonic.
I'm not quite sure what foo() is really supposed to do ... however the
built-in function setattr is your friend. Assuming that ini_dict
contains what you have scraped out of your .ini file, you can do:
x = MyCLass()
for key, value in ini_dict.items():
setattr(x, key, value)
You may prefer (I would) to do it inside the class, and maybe do some
checking/validation:
class MyClass(object):
def load(self, adict):
for k, v in adict.items():
# do checking here
setattr(self, k, v)
# much later
x = MyClass()
x.load(ini_dict)
HTH,
John
Hi John,
Your response is most helpful and informative -- thanks!
I don't think that setattr() is exactly what I need, though, as foo() doesn't
actually create or update its instance attributes. What I need to be able to
do is call foo() specifying keyword arguments not directly but viz a viz
another variable or variables that contain the keywords and values.
I'm pretty sure I just found the solution, which is to use the **-operator on
a dictionary. Actually, ConfigObj (the INI file reader) subclasses from
__builtin__.dict (i.e., the class/object *is* a dictionary), so the following
seems to work perfectly:
x.foo(**config)
This sends ALL the key/value pairs in config as keyword/value pairs to foo(),
which is exactly what I need.
Just FYI, I located this solution via Google shortly after posting, so I have
sent a cancel request on my original post.
Thanks again!
Doug
.
- References:
- Newbie: How can I use a string value for a keyword argument?
- From: Doug Morse
- Re: Newbie: How can I use a string value for a keyword argument?
- From: John Machin
- Newbie: How can I use a string value for a keyword argument?
- Prev by Date: Re: Newbie: How can I use a string value for a keyword argument?
- Next by Date: Re: Embedding a literal "\u" in a unicode raw string.
- Previous by thread: Re: Newbie: How can I use a string value for a keyword argument?
- Next by thread: Re: Newbie: How can I use a string value for a keyword argument?
- Index(es):
Relevant Pages
|
