Dictionary instantiation?

[Matt_D]

On Dec 7, 11:42 am, Virgil Dupras <hardcoded.softw... at gmail.com>
wrote:
> 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.

Another newb question, same project:

#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
        return csv_list

def author_to_dict(): #Function to add each author to the dictionary
once to get initial entry for that author
    #rem_blank_authors() #Call this function to remove blank author
fields before building the main dictionary
    for row in csv_file:
        author_count = row[-1]
        if author_count in story_per_author:
            story_per_author[author_count] += 1
        else:
            story_per_author[author_count] = 1
    return story_per_author

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

author_to_dict()
print story_per_author

--

The solution provided for my previous post worked out. Now I'm testing
the author_to_dict function, modified to get an accurate count of
stories each author has written. Now, if I call rem_blank_authors,
story_per_author == {}. But if I #comment out that line, it returns
the expected key values in story_per_author. What is happening in
rem_blank_authors that is returning no keys in the dictionary?

I'm afraid I don't really understand the mechanics of "return" and
searching the docs hasn't yielded too much help since "return" is such
a common word (in both the Python 2.5 docs and Dive Into Python). I
realize I should probably RTFM, but honestly, I have tried and can't
find a good answer. Can I get a down and dirty explanation of exactly
what "return" does? And why it's sometimes "return" and sometimes it
has an argument? (i.e. "return" vs. "return author_of_title")