[Tutor] Only appending one object to list, when I am expecting more than 1
AdamC
kabads at gmail.com
Tue Feb 26 09:39:55 EST 2019
Sorry folks - my code didn't work due to my debug var count to ensure that
I was looping properly.
It should be:
media = []
def loadFile():
filename = input('Filename? ')
f = open(filename, 'r')
createObjects(f)
def createObjects(f):
'''Takes a file object and iterates through entries, passing them to
create
object, depending on what object it is.'''
for line in f:
data = json.loads(line)
print(type(data['tpe']))
name = data['name']
platform = data['platform']
dateAdded = data['dateAdded']
tpe = data['tpe']
if data['tpe'] == 'Game':
a = createGame(name, platform, dateAdded,tpe)
game = {a: tpe}
media.append(game)
if data['tpe'] == 'Film':
a = createFilm(name, platform, dateAdded,tpe)
film = {a: tpe}
media.append(film)
# For some reason I'm only getting one object at a time now when
appending to media
print(len(media))
def createGame(name, platform, dateAdded, tpe):
return Game(name, platform, dateAdded)
def createFilm(name, platform, dateAdded, tpe):
return Film(name, platform, dateAdded)
Also, there is a bug that places an instance variable of dateAdded to tpe,
which is causing an error. This might be why I'm not getting more objects
than I expect.
My class is:
import datetime
class Media:
def __init__(self, name, platform, tpe):
self.name = name
self.platform = platform
date = datetime.datetime.now()
datestring = date.strftime("%Y:%m:%d:%H:%M:%s")
self.dateAdded = datestring
self.tpe = tpe
#self.dateAdded = datetime.datetime.now()
and
from . import media
#import media
class Game(media.Media):
#tpe = 'game'
# def __init__(self):
# self.type = 'game'
Thanks.
Adam
On Tue, 26 Feb 2019 at 10:02, Cameron Simpson <cs at cskk.id.au> wrote:
> Thank you for a well formed problem description.
>
> However, as Steven has remarked the code you've included doesn't run.
> Can you follow up/reply with your actual working script, and also
> include some of the output you get.
>
> That said, I've a few small remarks about the code you have posted:
>
> On 26Feb2019 09:09, AdamC <kabads at gmail.com> wrote:
> >I'm creating lots of objects from json in a file. Part of reading the json
> >back means that it iterates over the file and loads a json object and then
> >creates the object from the dictionary.
> >
> >This is my file:
> >
> >{"name": "Dwarf Fortress", "platform": "steam", "dateAdded":
> >"2019:02:25:16:56:1551113768", "tpe": "2019:02:21:13:49:1550756942"}
> >{"name": "Jaws", "platform": "Netflix", "dateAdded":
> >"2019:02:25:16:56:1551113768", "tpe": "2019:02:21:13:49:1550756960"}
> >{"name": "Wargames", "platform": "CLI", "dateAdded":
> >"2019:02:25:16:59:1551113984", "tpe": "Game"}
>
> BTW, I notice that only one of these rows has the "tpe" field set to
> "Game" or "Film", specificly the last one. So based on your code below,
> only one of these rows gets appended to the media array. Remarks below
> on writing code which is less prone to hiding this kind of problem.
>
> >and these are the functions that help load that file:
> >
> >media = []
> >
> >def loadFile():
> > filename = input('Filename? ')
> > f = open(filename, 'r')
> > createObjects(f)
>
> This f=open code would normally be written like this:
>
> with open(filename, 'r') as f:
> createObjects(f)
>
> That construction ensures that the file gets closed after running
> "createObjects()". As it is in your code the file is not explicitly
> closed; the CPython interpreter will, as it happens, close the file
> pretty promptly when "f" goes out of scope, but the language definition
> doesn't require such immediacy.
>
> >def createObjects(f):
> > '''Takes a file object and iterates through entries, passing them to
> >create
> > object, depending on what object it is.'''
> > for line in f:
> > count = count + 1
> > data = json.loads(line)
> > print(type(data['tpe']))
> > name = data['name']
> > platform = data['platform']
> > dateAdded = data['dateAdded']
> > tpe = data['tpe']
> > if data['tpe'] == 'Game':
> > a = createGame(name, platform, dateAdded,tpe)
> > game = {a: tpe}
> > media.append(game)
> > if data['tpe'] == 'Film':
> > a = createFilm(name, platform, dateAdded,tpe)
> > film = {a: tpe}
> > media.append(film)
>
> These if statements don't cover the case when "tpe" isn't "Game" or
> "Film", and (in other circumstances) could conceivably add two objects.
> If you construct it like this instead:
>
> if data['tpe'] == 'Game':
> a = createGame(name, platform, dateAdded,tpe)
> game = {a: tpe}
> media.append(game)
> elif data['tpe'] == 'Film':
> a = createFilm(name, platform, dateAdded,tpe)
> film = {a: tpe}
> media.append(film)
> else:
> print("Unhandled tpe value:", repr(tpe))
>
> then (a) only 1 branch can ever apply and (b) reports any unexpected
> values which would otherwise _silently_ get ignored. By always having a
> final "else" in an if/elif/..../else chain you can catch/observe these
> unhandled situations.
>
> >def createGame(name, platform, dateAdded, tpe):
> > return Game(name, platform, dateAdded)
> >
> >def createFilm(name, platform, dateAdded, tpe):
> > return Film(name, platform, dateAdded)
>
> Unless there's more stuff happening in these functions which you've
> stripped out for clarity you could just call the object constructors
> directly from the if statements:
>
> if data['tpe'] == 'Game':
> a = Game(name, platform, dateAdded)
> game = {a: tpe}
> media.append(game)
>
> >Why would I only get one object in media, even though all three are
> >created?
>
> As you may gather, all three input lines are processed, but only one
> gets turned into an object to add to media. Change the if/if into an
> if/elif/else and see if things become more obvious.
>
> Cheers,
> Cameron Simpson <cs at cskk.id.au>
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