[Tutor] Concatenating numeric data in Python 3.3

[Prasad, Ramit]

sparkle Plenty wrote:
> On Wed, Apr 24, 2013 at 4:21 PM, Prasad, Ramit <ramit.prasad at jpmorgan.com> wrote:
[snip]
> >
> > Here is my function as it stands now:
> >
> >   def conCatNumbers(numOne, numTwo, numThree):
> >     global instanceGroup, lengthCounter, instanceCounter
> >     print("Pre Pack:  ", numOne, " ", numTwo, " ", numThree)
> >     packValues = struct.pack("HBB", numOne, numTwo, numThree)
> >     print("Post Pack: ", packValues)
> >     instanceValues = (packValues, )
> >     print(instanceValues)
> >     instanceGroup = (instanceGroup, )
> >     instanceGroup = instanceGroup + instanceValues
> >     lengthCounter += 4
> >     instanceCounter += 1
> >     return (instanceGroup, lengthCounter, instanceCounter)
> >
[snip]
> >>> blah = []
> >>> def foo():
> ...     instanceValues = '\x04\xd2\x01\x00'
> ...     blah.append( instanceValues ) # module level object can be mutated without global keyword,
>                                       # just not reassigned (name binding).
> ...     print blah
> ...
[snip]
> ~Ramit
> 
> Thank you so much!  I knew the Global statement was a cop-out, but I was frustrated with the endless
> Unbounded Local Variable errors, and getting a little wild-eyed and desperate as my project deadline
> approaches.  I will implement the changes you suggested, and then retest.

Note that the above example is still using a global variable (actually a module level). 
You can eliminate it by just passing in the list as well.

def pack_without_globals(lst, numOne, numTwo, numThree):
    '''Pack values into hex bytes and append to lst.
    '''
    packValues = struct.pack("HBB", numOne, numTwo, numThree)
    lst.append( packValues )
    # No need to return lst because it is modified in place and the calling function should 
    # have access to the object anyway. 

> 
>  I have also searched the Tutor archives quite a lot, and noted a number of websites that I will
> peruse for another online course (I have taken the one at Python.org) so I can review class and
> function best practices.  It is great to have someone to ask when I get stuck.

That is the purpose of this list. :)


~Ramit


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