[Chicago] dict to local vars?

[Michael Tobis]

locals.update(mydict)

example:

>>> mydict = {"foo" : "bazz"}
>>> mydict["foo"]
'bazz'
>>> foo
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'foo' is not defined
>>> locals().update(mydict)
>>> foo
'bazz'



On Wed, Jan 22, 2014 at 2:22 PM, Adam Forsyth <adam at adamforsyth.net> wrote:

> I'll assume you know this is bad and that there are existing libraries to
> solve this problem.
>
>
> There isn't a good way to modify locals. Instead, I think you want to use
> the optional arguments to eval that allow you to provide dictionaries to
> use in place of the real locals and globals.
>
> import math
> def evaleq(eq,vals):
>     return 'expression '+eq+' => '+str(eval(eq,globals(),vals))
> myeq = 'a*math.log(b)'
> myvals = {'a':3, 'b':2}
> print evaleq(myeq,myvals)
> print evaleq('2*Abc',{'Abc':21.})
> print evaleq('2*Abc+a',{'Abc':21.})
>
> expression a*math.log(b) => 2.07944154168
> expression 2*Abc => 42.0
>
> Traceback (most recent call last):
>   File "eval.py", line 8, in <module>
>
>     print evaleq('2*Abc+a',{'Abc':21.})
>   File "eval.py", line 3, in evaleq
>     return 'expression '+eq+' => '+str(eval(eq,globals(),vals))
>
>   File "<string>", line 1, in <module>
> NameError: name 'a' is not defined
>
>
>
>
> On Wed, Jan 22, 2014 at 2:13 PM, Toby, Brian H. <toby at anl.gov> wrote:
>
>>  Can any Python gurus help me find a cleaner way to attack a problem? I
>> am of the opinion that *anything* can be done in Python (though not
>> always cleanly or wisely), but so far how to define variables in the local
>> namespace from a dict has so far eluded me.
>>
>>  Let me set the problem in context, in case there is a more pythonic way
>> to approach this task: I am working on a set of routines that will evaluate
>> an arbitrary expression. At least as I see myself framing the problem right
>> now, I will end up with a str with the equation and a dict containing the
>> values for each variable in the expression. I will not know what variable
>> names to expect in the expression, so I must deal with them as strings at
>> run-time.
>>
>>  I want to evaluate the expression reasonably quickly (as I will later
>> need numerical derivatives). The code fragment below does almost exactly
>> what I want, except the values end up in the module's global namespace, but
>> I would prefer they were in the local namespace or that of an object --- so
>> that the 3rd call to evaleq would produce an exception.
>>
>>   import numpy as np
>> def evaleq(eq,vals):
>>     for k,v in vals.iteritems(): globals()[k] = v
>>     return 'expression '+eq+' => '+str(eval(eq))
>> myeq = 'a*np.exp(b)'
>> myvals = {'a':1, 'b':0}
>> print evaleq(myeq,myvals)
>> print evaleq('2*Abc',{'Abc':21.})
>> print evaleq('2*Abc+a',{'Abc':21.})
>>
>>  Note that locals() is not supposed to be used in the way that I use
>> globals() above, at least as far as I understand, so that is not an option.
>>
>>  Any suggestions?
>>
>>  Brian
>>
>>  ********************************************************************
>> Brian H. Toby, Ph.D.                            office: 630-252-5488
>>  Senior Physicist/Section Head for Scientific Software
>>  Advanced Photon Source
>>  9700 S. Cass Ave, Bldg. 401/B4192
>>  Argonne National Laboratory
>>  Argonne, IL 60439-4856         e-mail: brian dot toby at anl dot gov
>>  ********************************************************************
>> "We will restore science to its rightful place, and wield technology's
>> wonders... We will harness the sun and the winds and the soil to fuel our
>> cars and run our factories...  All this we can do. All this we will do."
>>
>>
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>
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