Newbie: How can I use a string value for a keyword argument?
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. Thanks in advance for any and all assistance! Doug -- http://mail.python.org/mailman/listinfo/python-list
Re: Newbie: How can I use a string value for a keyword argument?
On Feb 25, 10:42 pm, Doug Morse [EMAIL PROTECTED] 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 -- http://mail.python.org/mailman/listinfo/python-list
Re: Newbie: How can I use a string value for a keyword argument?
On 25 Feb, 12:42, Doug Morse [EMAIL PROTECTED] 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
Try this:
y='trials'
x.foo( **{y:32} )
Ciao
-
FB
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Re: Newbie: How can I use a string value for a keyword argument?
Doug Morse a écrit :
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
You want something like:
x.foo(**{'trials':32})
Just for completeness, my goal is simply to read a bunch of key/value pairs
from an INI file (using ConfigObj)
ConfigObj being a subclass of dict, you should be able to use it
directly, ie:
x.foo(**my_config)
If just want to pass a section of the ConfigObj, it should work just the
same.
HTH
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Re: Newbie: How can I use a string value for a keyword argument?
On Mon, 25 Feb 2008 04:20:37 -0800 (PST), John Machin [EMAIL PROTECTED] wrote: On Feb 25, 10:42 pm, Doug Morse [EMAIL PROTECTED] 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 -- http://mail.python.org/mailman/listinfo/python-list
Re: Newbie: How can I use a string value for a keyword argument?
Doug Morse 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
Keyword args are represented during the calling process as a
dictionary, You can create the dictionary yourself, and slip it into
the calling arguments with a ** notation:
kw = {somestring:32}
x.foo(**kw)
Gary Herron
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.
Thanks in advance for any and all assistance!
Doug
--
http://mail.python.org/mailman/listinfo/python-list
