create global variables?

J. Clifford Dyer jcd at sdf.lonestar.org
Mon Oct 30 18:56:18 CET 2006


Alistair King wrote:
> Hi,
> 
> is there a simple way of creating global variables within a function?
> 
> ive tried simply adding the variables in:
> 
> def function(atom, Xaa, Xab):
>     Xaa = onefunction(atom)
>     Xab = anotherfunction(atom)
> 
> if i can give something like:
> 
> function('C')    #where atom = 'C' but not necessarly include Xaa or Xab
> 
> i would like to recieve:
> 
> Caa = a float
> Cab = another float
> 
> ive tried predefining Xaa and Xab before the function but they are
> global values and wont change within my function. Is there a simple way
> round this, even if i call the function with the variables ('C', Caa, Cab)?
> ...............................................................................................................................
> 
> some actual code:
> 
> # sample dictionaries
> DS1v = {'C': 6}
> pt = {'C': 12.0107}
> 
> def monoVarcalc(atom):
>     a = atom + 'aa'
>     Xaa = a.strip('\'')
>     m = atom + 'ma'
>     Xma = m.strip('\'')
>     Xaa = DS1v.get(atom)
>     Xma = pt.get(atom)
>     print Xma
>     print Xaa
> 
> monoVarcalc('C')
> 
> print Caa
> print Cma
> ...............................................................................................................................
> it seems to work but again i can only print the values of Xma and Xaa
> 
> ?
> 
> Alistair
> 

I suspect you are misusing the concept of a function.  In most basic 
cases, and I suspect your case applies just as well as most, a function 
should take arguments and return results, with no other communication 
between the calling code and the function itself.  When you are inside 
your function don't worry about the names of the variables outside.  I'm 
not sure exactly where your floats are coming from, but try something 
like this:

 >>> def monoVarCalc(relevant_data):
...     float1 = relevant_data * 42.0
...     float2 = relevant_data / 23.0
...     return float1, float2

 >>> C = 2001
 >>> Caa, Cab = monoVarCalc(C)
 >>> Caa
84042.0
 >>> Cab
87.0

Notice that you don't need to use the variable C (or much less the 
string "C", inside monoVarCalc at all.  It gets bound to the name 
relevant_data instead.

Also, if you are going to have a lot of these little results lying 
around, (Cab, Cac ... Czy, Czz), you might consider making them a list 
or a dictionary instead.  I won't tell you how to do that, though.  The 
online tutorial has plenty of information on that.

http://docs.python.org/tut/tut.html


Cheers,
Cliff



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