Create an Art Marketplace - Veneer Project

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1

My code will generate an error and I cannot find the mistake, even though watching the Project Walkthrough. I’ve been banging my head against the wall for a couple of hours now. Any help will be greatly appreciated. The error:

Traceback (most recent call last):
File “script.py”, line 110, in
veneer.show_listings()
File “script.py”, line 35, in show_listings
print(listing)
TypeError: str returned non-string (type NoneType)

The code:

# 2.
class Art():
  # 3.
  # 19a.
  def __init__(self, artist, title, medium, year, owner):
    self.artist = artist
    self.title = title
    self.medium = medium
    self.year = year
    # 19b.
    self.owner = owner

  # 4.
  # 20.
  def __repr__(self):
    return '{artist}. "{title}\". {year}, {medium}. {owner_name}, {owner_location}.'.format(artist = self.artist, title = self.title, year = self.year, medium = self.medium, owner_name = self.owner.name, owner_location = self.owner.location)

# 7.
class Marketplace():
  # 8.
  def __init__(self):
    self.listings = []

  # 9.
  def add_listing(self, new_listing):
    self.listings.append(new_listing)
  
  # 10.
  def remove_listing(self, remove_listing):
    self.listings.remove(remove_listing)
  
  # 11.
  def show_listings(self):
    for listing in self.listings:
      print(listing)

# 14.
class Client():
  # 15.
  def __init__(self, name, location, is_museum):
    self.name = name
    self.is_museum = is_museum
    if is_museum:
      self.location = location
    else:
      self.location = 'private Collection'
  
  # 26.
  def sell_artwork(self, artwork, price):
    if self == artwork.owner:
      new_listing = Listing(artwork, price, self)
      veneer.add_listing(new_listing)
      print('listing added')
    else:
      print('The selling client is not the artwork owner')

  # 29.
  def buy_artwork(self, artwork):
    if self != artwork.owner:
      art_listing = None
    # 30.
    for listing in veneer.listings:
      if listing.art == artwork:
       art_listing = listing
       break
    # 31.
    artwork.owner = self
    veneer.remove_listing(art_listing)

# 23.
class Listing:
  # 24.
  def __init__(self, art, price, seller):
    self.art = art
    self.price = price
    self.seller = seller

  # 25.
  def __repr__(self):
    print('{art}, {price}'.format(art = self.art.title, price = self.price))

# 5.
# girl_with_mandolin = Art('Picasso, Pablo', 'Girl with a Mandolin (Fanny Tellier)', 'oil on canvas', '1910')

# 6.
# print(girl_with_mandolin)

# 12.
veneer = Marketplace()

# 13.
veneer.show_listings()

# 16.
edytta = Client('Edytta Halpirt', None, False)

# 17.
moma = Client('The MOMA', 'New York', True)

# 21.
girl_with_mandolin = Art('Picasso, Pablo', 'Girl with a Mandolin (Fanny Tellier)', 'oil on canvas', '1910', edytta)

# 22.
print(girl_with_mandolin)

# 27.
edytta.sell_artwork(girl_with_mandolin, '$6M (USD)')

# 28.
veneer.show_listings()

# 32.
moma.buy_artwork(girl_with_mandolin)

# 33.
print(girl_with_mandolin)

# 34.
veneer.show_listings()
2

I’ve not checked in detail but I believe you have an issue with the Listing class and an in particular __repr__(). Check up on how __repr__ should be used.

3

Thank you so much! Greatly appreciated!
As usual it’s so simple. I’m just insufficiently experienced at interpreting the errors.
My definition of the .repr() method generates None instead of a string. Just replace print with return and presto.
It’s a good thing, I can enjoy my own coding mistakes even though they cost me hours.
Thanks again!

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