converting a string to a function parameter

Hi,
Is it possible to convert a string to a function parameter?
Ex:
str = 'True, type=rect, sizes=[3, 4]'
and I should be able to use it as:
test(convert(str)) and the behaviour should be same as calling test
with those values :
i.e. test(True, type=rect, sizes=[3, 4])

I tried eval, but it did not work. And any other mechanism I think
turns out to be creating a full fledged python parser.

Is there any mechanism with which we can do this straight away?

On Fri, Mar 13, 2009 at 12:52 AM, koranthala <koranthala@gmail.com> wrote:
> Hi,
> Â* Â*Is it possible to convert a string to a function parameter?
> Ex:
> str = 'True, type=rect, sizes=[3, 4]'
> and I should be able to use it as:
> test(convert(str)) and the behaviour should be same as calling test
> with those values :
> i.e. test(True, type=rect, sizes=[3, 4])
>
> I tried eval, but it did not work. And any other mechanism I think
> turns out to be creating a full fledged python parser.
>
> Is there any mechanism with which we can do this straight away?

Firstly, don't use `str` as a variable name since it conflicts with
the name of the builtin type.

Now here's how to use eval() properly:

[insert standard 'eval() is EVIL!' warning/lecture here]

eval("test("+the_str+")")

or

eval(test.__name__+"("+the_str+")")

Cheers,
Chris

--
I have a blog:
http://blog.rebertia.com

On Mar 13, 1:01*pm, Chris Rebert <c...@rebertia.com> wrote:
> On Fri, Mar 13, 2009 at 12:52 AM, koranthala <koranth...@gmail.com> wrote:
> > Hi,
> > * *Is it possible to convert a string to a function parameter?
> > Ex:
> > str = 'True, type=rect, sizes=[3, 4]'
> > and I should be able to use it as:
> > test(convert(str)) and the behaviour should be same as calling test
> > with those values :
> > i.e. test(True, type=rect, sizes=[3, 4])
>
> > I tried eval, but it did not work. And any other mechanism I think
> > turns out to be creating a full fledged python parser.
>
> > Is there any mechanism with which we can do this straight away?
>
> Firstly, don't use `str` as a variable name since it conflicts with
> the name of the builtin type.
>
> Now here's how to use eval() properly:
>
> [insert standard 'eval() is EVIL!' warning/lecture here]
>
> eval("test("+the_str+")")
>
> or
>
> eval(test.__name__+"("+the_str+")")
>
> Cheers,
> Chris
>
> --
> I have a blog:http://blog.rebertia.com

Thank you very much Chris.
I also thought about the first method a second after I posted this.
But I never thought about the second method.
I will heed the warning about the str part.

Thank you very much again, Chris.

On Mar 13, 12:52*am, koranthala <koranth...@gmail.com> wrote:
> Hi,
> * * Is it possible to convert a string to a function parameter?
> Ex:
> str = 'True, type=rect, sizes=[3, 4]'
> and I should be able to use it as:
> test(convert(str)) and the behaviour should be same as calling test
> with those values :
> i.e. test(True, type=rect, sizes=[3, 4])
>
> I tried eval, but it did not work. And any other mechanism I think
> turns out to be creating a full fledged python parser.
>
> Is there any mechanism with which we can do this straight away?

If the string has all of the names you could parse it into a
dictionary and pass it as the keyword arguments

koranthala wrote:
> Hi,
> Is it possible to convert a string to a function parameter?
> Ex:
> str = 'True, type=rect, sizes=[3, 4]'
> and I should be able to use it as:
> test(convert(str)) and the behaviour should be same as calling test
> with those values :
> i.e. test(True, type=rect, sizes=[3, 4])
>
> I tried eval, but it did not work. And any other mechanism I think
> turns out to be creating a full fledged python parser.

This might work [again be avoid eval if possible].
You _might want to do something like:

def _args(*_nargs, **_kwargs):
'''Collect call parameters from a call'''
return _nargs, _kwargs
...
nargs, kwargs = eval('_args(%s)' % arglist
...
test(*nargs, **kwargs)

--Scott David Daniels
Scott.Daniels@Acm.Org

On Mar 13, 2:52*am, koranthala <koranth...@gmail.com> wrote:
> Hi,
> * * Is it possible to convert a string to a function parameter?
> Ex:
> str = 'True, type=rect, sizes=[3, 4]'
> and I should be able to use it as:
> test(convert(str)) and the behaviour should be same as calling test
> with those values :
> i.e. test(True, type=rect, sizes=[3, 4])
>
> I tried eval, but it did not work. And any other mechanism I think
> turns out to be creating a full fledged python parser.
>
> Is there any mechanism with which we can do this straight away?

I heard 'pyparsing' was good. ...Not that I've even been to its
webpage.

On Mar 13, 11:46*am, Aaron Brady <castiro...@gmail.com> wrote:
> On Mar 13, 2:52*am, koranthala <koranth...@gmail.com> wrote:
>
> > Hi,
> > * * Is it possible to convert a string to a function parameter?
> > Ex:
> > str = 'True, type=rect, sizes=[3, 4]'
> > and I should be able to use it as:
> > test(convert(str)) and the behaviour should be same as calling test
> > with those values :
> > i.e. test(True, type=rect, sizes=[3, 4])
>
> > I tried eval, but it did not work. And any other mechanism I think
> > turns out to be creating a full fledged python parser.
>
> > Is there any mechanism with which we can do this straight away?
>
> I heard 'pyparsing' was good. *...Not that I've even been to its
> webpage.

Did someone say 'pyparsing'? Here is a first cut (partially lifted
from a previous post):


from pyparsing import *

LPAR,RPAR,LBRACK,RBRACK,EQ,COMMA = map(Suppress,"()[]=,")

noneLiteral = Literal("None")
boolLiteral = oneOf("True False")
integer = Combine(Optional(oneOf("+ -")) + Word(nums)).setName
("integer")
real = Combine(Optional(oneOf("+ -")) + Word(nums) + "." +
Optional(Word(nums))).setName("real")

ident = Word(alphas+"_",alphanums+"_")

listStr = Forward().setName("list")
tupleStr = Forward().setName("tuple")
listItem = real | integer | noneLiteral | boolLiteral | \
quotedString.setParseAction(removeQuotes) | Group(listStr) |
tupleStr | ident
listStr << ( LBRACK + Optional(delimitedList(listItem)) + Optional
(COMMA) + RBRACK )
tupleStr << (LPAR + Optional(delimitedList(listItem)) + Optional
(COMMA) + RPAR)

# parse actions perform parse-time conversions
noneLiteral.setParseAction(lambda: None)
boolLiteral.setParseAction(lambda toks: toks[0]=="True")
integer .setParseAction(lambda toks: int(toks[0]))
real .setParseAction(lambda toks: float(toks[0]))
listStr .setParseAction(lambda toks: toks.asList())
tupleStr .setParseAction(lambda toks: tuple(toks.asList()))

arg = Group(ident("varname") + EQ + listItem("varvalue")) | listItem


argstring = 'True, type=rect, sizes=[3, 4,], coords = ([1,2],[3,4])'

parsedArgs = delimitedList(arg).parseString(argstring)
args = []
kwargs = {}
for a in parsedArgs:
if isinstance(a,ParseResults):
if isinstance(a.varvalue,ParseResults):
val = a.varvalue.asList()
else:
val = a.varvalue
kwargs[a.varname] = val
else:
args.append(a)

print "Args:", args
print "Kwargs:", kwargs


Prints:

Args: [True]
Kwargs: {'coords': ([1, 2], [3, 4]), 'type': 'rect', 'sizes': [3, 4]}

On Mar 13, 3:21*pm, Paul McGuire <pt...@austin.rr.com> wrote:
> On Mar 13, 11:46*am, Aaron Brady <castiro...@gmail.com> wrote:
>
>
>
> > On Mar 13, 2:52*am, koranthala <koranth...@gmail.com> wrote:
>
> > > Hi,
> > > * * Is it possible to convert a string to a function parameter?
> > > Ex:
> > > str = 'True, type=rect, sizes=[3, 4]'
> > > and I should be able to use it as:
> > > test(convert(str)) and the behaviour should be same as calling test
> > > with those values :
> > > i.e. test(True, type=rect, sizes=[3, 4])
>
> > > I tried eval, but it did not work. And any other mechanism I think
> > > turns out to be creating a full fledged python parser.
>
> > > Is there any mechanism with which we can do this straight away?
>
> > I heard 'pyparsing' was good. *...Not that I've even been to its
> > webpage.
>
> Did someone say 'pyparsing'? *Here is a first cut (partially lifted
> from a previous post):
snip 40 lines
> Prints:
>
> Args: [True]
> Kwargs: {'coords': ([1, 2], [3, 4]), 'type': 'rect', 'sizes': [3, 4]}

Ha, ok, out of my league. It's a bit heavyweight I accede. The OP
didn't say what s/he knew about his/er data prior, what fault
tolerance s/he needed, what complexity and nesting of data in the
string, etc.

Hmmm..., just thinking. Could the strings come from a python file:
test1= fargs(True, type=rect, sizes=[3, 4])
test2= fargs(...)
?

I'm a bit late to the party, but LEPL 2.2, just released, can now handle
this too. I suspect email may mangle this, so you can also read it at
http://www.acooke.org/lepl/examples....-argument-list


from lepl import *

comma = Drop(',')
none = Literal('None') >> (lambda x: None)
bool = (Literal('True') | Literal('False')) >> (lambda x: x == 'True')
ident = Word(Letter() | '_',
Letter() | '_' | Digit())
float_ = Float() >> float
int_ = Integer() >> int
str_ = String() | String("'")
item = str_ | int_ | float_ | none | bool | ident

with Separator(~Regexp(r'\s*')):
value = Delayed()
list_ = Drop('[') & value[:, comma] & Drop(']') > list
tuple_ = Drop('(') & value[:, comma] & Drop(')') > tuple
value += list_ | tuple_ | item
arg = value >> 'arg'
karg = (ident & Drop('=') & value > tuple) >> 'karg'
expr = (karg | arg)[:, comma] & Drop(Eos()) > Node

parser = expr.string_parser()

ast = parser('True, type=rect, sizes=[3, 4], coords = ([1,2],[3,4])')
print(ast[0])


which gives:

Node
+- arg True
+- karg (u'type', u'rect')
+- karg (u'sizes', [3, 4])
`- karg (u'coords', ([1, 2], [3, 4]))

you can then access those values:
>>> ast[0].arg
[True]
>>> ast[0].karg
[('type', 'rect'), ('sizes', [3, 4]), ('coords', ([1, 2], [3, 4]))]

alternatively, you could avoid using a Node altogether and just put them
in a list or whatever....

andrew



Paul McGuire wrote:
> from pyparsing import *
>
> LPAR,RPAR,LBRACK,RBRACK,EQ,COMMA = map(Suppress,"()[]=,")
>
> noneLiteral = Literal("None")
> boolLiteral = oneOf("True False")
> integer = Combine(Optional(oneOf("+ -")) + Word(nums)).setName
> ("integer")
> real = Combine(Optional(oneOf("+ -")) + Word(nums) + "." +
> Optional(Word(nums))).setName("real")
>
> ident = Word(alphas+"_",alphanums+"_")
>
> listStr = Forward().setName("list")
> tupleStr = Forward().setName("tuple")
> listItem = real | integer | noneLiteral | boolLiteral | \
> quotedString.setParseAction(removeQuotes) | Group(listStr) |
> tupleStr | ident
> listStr << ( LBRACK + Optional(delimitedList(listItem)) + Optional
> (COMMA) + RBRACK )
> tupleStr << (LPAR + Optional(delimitedList(listItem)) + Optional
> (COMMA) + RPAR)
>
> # parse actions perform parse-time conversions
> noneLiteral.setParseAction(lambda: None)
> boolLiteral.setParseAction(lambda toks: toks[0]=="True")
> integer .setParseAction(lambda toks: int(toks[0]))
> real .setParseAction(lambda toks: float(toks[0]))
> listStr .setParseAction(lambda toks: toks.asList())
> tupleStr .setParseAction(lambda toks: tuple(toks.asList()))
>
> arg = Group(ident("varname") + EQ + listItem("varvalue")) | listItem
>
>
> argstring = 'True, type=rect, sizes=[3, 4,], coords = ([1,2],[3,4])'
>
> parsedArgs = delimitedList(arg).parseString(argstring)
> args = []
> kwargs = {}
> for a in parsedArgs:
> if isinstance(a,ParseResults):
> if isinstance(a.varvalue,ParseResults):
> val = a.varvalue.asList()
> else:
> val = a.varvalue
> kwargs[a.varname] = val
> else:
> args.append(a)
>
> print "Args:", args
> print "Kwargs:", kwargs
>
>
> Prints:
>
> Args: [True]
> Kwargs: {'coords': ([1, 2], [3, 4]), 'type': 'rect', 'sizes': [3, 4]}
>
> --
> http://mail.python.org/mailman/listinfo/python-list
>
>