Matt_D a écrit :
> 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
First point: your comment would be better in a docstring - and that
would make the code more readable
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:
Second point: you're using 2 global variables. This is something to
avoid whenever possible (that is: almost always). Here you're in the
very typical situation of a function that produces output
(story_per_author) depending only on it's input (csv_file) - so the
correct implementation is to pass the input as an argument and return
the output:
> author_count = row[-1]
> story_per_author[author_count] = 1
def author_to_dict(csv_file):
story_per_author = {}
for row in csv_file:
author_count = row[-1]
story_per_author[author_count] = 1
return story_per_author
Now take care: the object returned by csv.reader is not a sequence, it's
an iterator. Once you've looped over all it's content, it's exhausted.
> #Fetch author names
> def rem_blank_authors():
same remark wrt/ comments
#Function to remove entries with '' in the
> AUTHOR field of the .csv
# Convert the open file to list format
# for e-z mode editing
> csv_list = list(csv_file)
Yet another useless global.
> 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
Since you don't return anything from this function, the only effect is
to consume the whole global csv_file iterator - the csv_list object is
discarded after function execution.
> 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
Same remarks here
>
> assign_author_to_title()
> print author_of_title
author_of_title is local to the assign_author_to_title function. You
cannot access it from outside.
> --
>
> 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):
22> 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?
Bingo.
> The concept of instantiation is
> sort of foreign to me so I'm having some trouble predicting when it
> happens.
It has nothing to do with instanciation, it's about scoping rules. A
named defined in a function is local to that function. If you create an
object in a function and want to make it available to the outside world,
you have to return it from the function - like I did the rewrite of
author_to_dict - and of course assign this return value to another name
in the caller function scope.
> 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?
By all mean avoid global variables. In all the above code, there's not a
single reason to use them. Remember that functions take params and
return values. Please take a little time to read more material about
functions and scoping rules.
> 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
Well... It might be better !-)
Ok, there are the usual CS-newbie-struggling-with-new-concepts errors.
The cure is well-known : read more material (tutorials and code),
experiment (Python is great for this - read about the '-i' option of the
python interpreter), and post here when you run into trouble.
> but please be gentle!
Hope I haven't been to rude !-)
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