[Chicago] dict to local vars?

[Michael Tobis]

oops I mean

locals().update(mydict)


On Wed, Jan 22, 2014 at 3:35 PM, Michael Tobis <mtobis at gmail.com> wrote:

> 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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>
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