Python checking already exists element in list

Question

I would like to make sure that the same film is added, but unfortunately, something is not working out. What am I doing wrong?

class Movie:
    def __init__(self, name, pegi, year):
        self.name = name
        self.pegi = pegi
        self.year = year

class Movies(Movie):

    def __init__(self):
        self.collection = []

    def addMovieToCollection(self, name, pegi, year):
        super().__init__(name, pegi, year)
        structure_of_movie = name + " - " + pegi + " - " + str(year)
        if structure_of_movie in self.collection :
            print("That movie like" + self.name + " already exists")
        else:
            self.collection.append(structure_of_movie)

    def showMovie(self):
        return print(*self.collection, sep='\n')

f = Movies()

f.addMovieToCollection("Iron Man 1", "blue sign", 1995)
f.addMovieToCollection("Iron Man 1", "blue sign", 1995)
f.addMovieToCollection("Iron Man 2", "+7", 1995)
f.addMovieToCollection("Iron Man 3", "+16", 1995)
f.addMovieToCollection("Iron Man 4", "+12", 1995)
f.addMovieToCollection("Iron Man 5", "+18", 1995)
f.showMovie()

Please Help me

"something is not working" what is not working? How someone can understand what do you mean by "something" you should tell exactly what is not working — deadshot, Nov 28 '20 at 08:49
the security of adding the same film does not work - foreach loop — powezka43, Nov 28 '20 at 08:51
You don't want to let the same film be added twice correct ? and the uniqueness check is only on the film name? not in the film name + year ? — Vikash Singh, Nov 28 '20 at 08:52
this will help [Compare object instances for equality by their attributes](https://stackoverflow.com/questions/1227121/compare-object-instances-for-equality-by-their-attributes) — deadshot, Nov 28 '20 at 08:52
@VikashSingh I would like to get it, but for now it does not work with the name itself — powezka43, Nov 28 '20 at 08:54
I mean, `self.collection.__eq__(CurrentFilm)` is going to compare the _whole_ `collection` to each of the films in it. It's like comparing a basket of apples to one single apple - they will _never_ be equal — ForceBru, Nov 28 '20 at 08:54
As an aside, `super().__init__(name, pegi, year)` makes no sense in `addMovieToCollection`. And having `Movies` inherit from `Movie` also makes no sense. — juanpa.arrivillaga, Nov 28 '20 at 08:59
@juanpa.arrivillaga so how do you inherit the constructor from the `Movie` class? — powezka43, Nov 28 '20 at 09:05
@powezka43 *in the constructor usually*. Why would you call the constructor every time you use `addMovieToCollection`? But again, *fundamentally* having `Movies` inherit from `Movie` is a broken design. A thing is not a collection of things. A collection of things *has things*. A collection of things is a separate type. Just *don't inherit* from `Movie` at all. Use *composition*, not inheritance. — juanpa.arrivillaga, Nov 28 '20 at 09:06
@powezka43 Didn't you just update the question with working code from one of the answers? Why would you do that? Now the question "what am I doing wrong" makes 0 sense because the code works as expected and there is nothing _wrong_ with it. Could you please revert to the original code, clarify your question (provide expected and actual output) and mark the answer as accepted if it fixed your problem? — Czaporka, Nov 28 '20 at 09:24

Vikash Singh · Accepted Answer · 2020-11-28T09:40:43.003

Add __eq__ and __hash__ method in class, something like this:

class Movie:
    def __init__(self, name, pegi, year):
        self.name = name
        self.pegi = pegi
        self.year = year

    def __eq__(self, other): 
        if not isinstance(other, Movie):
            # don't attempt to compare against unrelated types
            return NotImplemented

        return self.name == other.name # and self.year == other.year
    
    def __hash__(self):
        return hash(self.name)
        # if you want to compare with year too.
        # return hash(self.name + str(self.year))   
      
    def __str__(self):
        # This is how each movie will be printed. 
        # You can improve the formatting here.
        return "Movie name: {}, Year: {}".format(self.name, self.year)

class Movies(): # it makes no sense that Movies should inherit Movie, don't do that.

    def __init__(self):
        self.collection = set()

    def addMovieToCollection(self, name, pegi, year):
        current_movie = Movie(name, pegi, year)
        if current_movie in self.collection:
            print("That movie like" + current_movie.name + " already exists")
        else:
            self.collection.add(current_movie)
            print("Added " + current_movie.name + " " + str(current_movie.year))
            
    def __str__(self):
        # Join the collection together how you would like to represent it.
        response = "\nMovies Collection:\n"
        for movie in self.collection:
            response += str(movie) + "\n"
        return response

f = Movies()

f.addMovieToCollection("Iron Man 1", "blue sign", 1995)
f.addMovieToCollection("Iron Man 2", "+7", 1995)
f.addMovieToCollection("Iron Man 1", "blue sign", 1996)
f.addMovieToCollection("Iron Man 1", "blue sign", 1995)
print(f)

output:

Added Iron Man 1 1995
Added Iron Man 2 1995
That movie likeIron Man 1 already exists
That movie likeIron Man 1 already exists

Movies Collection:
Movie name: Iron Man 2, Year: 1995
Movie name: Iron Man 1, Year: 1995
Iron Man 11995

Finally to print the movies I would advise you implement __str__ method in both classes. Movie class __str__ should return 1 movie. and Movies class __str__ should return the list of movie.

Hope this helps.

Yeah, that's help me but __str__ cant return me list of movies — powezka43, Nov 28 '20 at 09:19
I tried but i have `TypeError: __str__ returned non-string (type set)` — powezka43, Nov 28 '20 at 09:23
You need to loop on the values and convert them individually to str and return that string after joining, updated the code with this. — Vikash Singh, Nov 28 '20 at 09:26
No not at all, you are only getting started, things will get better with time. Trust me and hang in there :) Keep practicing. PS: Also if possible accept the answer by clicking on the Tick mark if it helped you and upvoting :D — Vikash Singh, Nov 28 '20 at 09:43
I had a 4 month break in programming (I was also learning JS and not Python) and maybe it makes me confused. — powezka43, Nov 28 '20 at 09:51
possible JS and python could be difficult to process together. But I would suggest you keep at it. You will get it in the end, keep solving problems :) All the very best. — Vikash Singh, Nov 28 '20 at 09:56
Thank you, I think JS is 'biting' me with Python. Greetings :) — powezka43, Nov 28 '20 at 09:59

score 0 · Answer 2 · answered Nov 28 '20 at 08:54

I thinks this will resolve your issue. Let me know if you meant something else.

class Movie:
    def __init__(self, name, pegi, year):
        self.name = name
        self.pegi = pegi
        self.year = year

class Movies(Movie):

    def __init__(self):
        self.collection = []

    def addMovieToCollection(self, name, pegi, year):
        super().__init__(name, pegi, year)
        structure_of_movie = name + " - " + pegi + " - " + str(year)
        #I removed the for loop here
        if structure_of_movie in self.collection : #IChanged this if condition as well
            print("That movie like" + self.name + " already exists")
        else:
            self.collection.append(structure_of_movie)

    def showMovie(self):
        return print(*self.collection, sep='\n')

f = Movies()

f.addMovieToCollection("Iron Man 1", "blue sign", 1995)
f.addMovieToCollection("Iron Man 1", "blue sign", 1995)
f.addMovieToCollection("Iron Man 2", "+7", 1995)
f.addMovieToCollection("Iron Man 3", "+16", 1995)
f.addMovieToCollection("Iron Man 4", "+12", 1995)
f.addMovieToCollection("Iron Man 5", "+18", 1995)
f.showMovie()

Not a downvoter. But when you posting answer you should explain how your answer solves the OP problem — deadshot, Nov 28 '20 at 09:00
Thanks for the info but i did mention the changes in the code and the rest was same code that i used which was there in the question. sow what else was needed to explain...just help me with this one more piece of info — Sachin Rajput, Nov 28 '20 at 09:23

Python checking already exists element in list

2 Answers2