So I thought I had come to peace with binding in Python, but then this
happened to me:
I was trying to do things the Python way (as opposed to the Scheme way)
as was suggested to me, and so here's a shortened version of my program:
def getGenres(title ): #it takes a movie title and returns a list of
genres that the movie falls into
result = [] # my accumulator
def inGenre(g): # g is a genre
if <here I test if "title" is of genre g (using a simple Python
dictionary I have collected from a mini web crawl)>:
result = result + [g] # if title is of genre g, then add
it to the accumulator
# and then I do a number of inGenre tests:
inGenre('Comedy ')
inGenre('Sci-fi')
inGenre('Suspen se')
...
return result
So what's wrong with this program? Well, Python tells me:
UnboundLocalErr or: local variable 'result' referenced before assignment
It seems my only choice is to move result to the global environment,
but if that's not a kludge, I don't know what is. So why doesn't this
work? Python lambdas are able to use "free" variables in this way.
Why not a def? And more importantly, how should I get around this?
Thanks all,
Rob 2 1477
Rob Hunter <ro*@cs.brown.e du> wrote:
.... def getGenres(title ): #it takes a movie title and returns a list of genres that the movie falls into
result = [] # my accumulator
def inGenre(g): # g is a genre if <here I test if "title" is of genre g (using a simple Python dictionary I have collected from a mini web crawl)>: result = result + [g] # if title is of genre g, then add
Here you're attempting to rebind a variable which lives in an
enclosing scope. This isn't possible in Python (except for globals).
Use result.append(g ) instead and it should work.
"Rob Hunter" <ro*@cs.brown.e du> wrote in message
news:ma******** *************** ***********@pyt hon.org... def inGenre(g): # g is a genre if <here I test if "title" is of genre g (using a simple
Python dictionary I have collected from a mini web crawl)>: result = result + [g] # if title is of genre g, then
add it to the accumulator
UnboundLocalErr or: local variable 'result' referenced before
assignment
When, within a function, you assign to a variable that has not been
declared global, then you implicitly declare that variable to be local
to the function -- in this case, inGenre(). But local var 'result'
has not previously been assigned a value within inGenre. Hence the
error message. As JCM said, try result.append(g ).
Terry J. Reedy This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
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