Dictionary instantiation?

[Virgil Dupras]

On Dec 7, 9:05 am, Matt_D <matt.debo... at gmail.com> wrote:
> Hello there, this is my first post to the list. Only been working with
> Python for a few days. Basically a complete newbie to programming.
>
> I'm working with csv module as an exercise to parse out a spreadsheet
> I use for work.(I am an editor for a military journalism unit) Not
> trying to do anything useful, just trying to manipulate the data.
> Anyway, here's the code I've got so far:
>
> import csv
> import string
> import os
>
> #Open the appropriate .csv file
> csv_file = csv.reader(open("D:\\Python25\\BNSR.csv"))
>
> #Create blank dictionary to hold {[author]:[no. of stories]} data
> story_per_author = {}
>
> def author_to_dict(): #Function to add each author to the dictionary
> once to get initial entry for that author
>     for row in csv_file:
>         author_count = row[-1]
>         story_per_author[author_count] = 1
>
> #Fetch author names
> def rem_blank_authors(): #Function to remove entries with '' in the
> AUTHOR field of the .csv
>     csv_list = list(csv_file) #Convert the open file to list format
> for e-z mode editing
>     for row in csv_list:
>         author_name = row[-1]
>         if author_name == '': #Find entries where no author is listed
>             csv_list.remove(row) #Remove those entries from the list
>
> def assign_author_to_title(): #Assign an author to every title
>     author_of_title = {}
>     for row in csv_file:
>         title = row[3]
>         author = row[-1]
>         author_of_title[title] = author
>
> assign_author_to_title()
> print author_of_title
>
> --
>
> Ok, the last two lines are kind of my "test the last function" test.
> Now when I run these two lines I get the error:
>
> Traceback (most recent call last):
>   File "D:\Python25\Lib\SITE-P~1\PYTHON~1\pywin\framework
> \scriptutils.py", line 310, in RunScript
>     exec codeObject in __main__.__dict__
>   File "D:\Python25\csv_read.py", line 33, in <module>
>     print author_of_title
> NameError: name 'author_of_title' is not defined
>
> I am guessing that the author_of_title dict does not exist outside of
> the function in which it is created? The concept of instantiation is
> sort of foreign to me so I'm having some trouble predicting when it
> happens.
>
> If I call the assign_author_to_title function later, am I going to be
> able to work with the author_of_title dictionary? Or is it best if I
> create author_of_title outside of my function definitions?
>
> Clearly I'm just stepping through my thought process right now,
> creating functions as I see a need for them. I'm sure the code is
> sloppy and terrible but please be gentle!

As you said, author_of_title doesn't exist outside of
assign_author_to_title() because it has been instantiated in the
function, and thus belong to the local scope. You could instantiate
your dictionary outside of the function, but the nicest way to handle
this would be to add a line "return author_of_title" at the end of
assign_author_to_title() and have "print assign_author_to_title()"
instead of the 2 last lines.