CODEWITHSUNDEEP
pythondjango
Aleksei Khatkevich
Aleksei Khatkevich

Reputation: 2197

count() method of the list class applied to queryset. Strange behaviour. Django

Cant find out why I keep getting following following error:

TypeError at /boats/reversion/ count() takes 1 positional argument but 2 were given

#views
…
…
…

memory_limiter = BoatImage.objects.filter(boat_id__isnull=True).exclude(
    memory__in=existing_boats_pk).values_list("memory", flat=True)

for i in memory_limiter:
    if memory_limiter.count(i)  >  3:
        memory_limiter.remove(i)

what shell says about memory limiter:


>>> for memory in memory_limiter:
...     print(memory, type(memory))
...
93 <class 'int'>
93 <class 'int'>
93 <class 'int'>
93 <class 'int'>
93 <class 'int'>
93 <class 'int'>
93 <class 'int'>
100 <class 'int'>
102 <class 'int'>
102 <class 'int'>
102 <class 'int'>
>>> memory_limiter
<QuerySet [93, 93, 93, 93, 93, 93, 93, 100, 102, 102, 102]>
>>>

following method brings same results:


for i in [ x for x in memory_limiter]:
    if memory_limiter.count(i) > 3:
        memory_limiter.remove(i)

Question is whats wrong with the count? I copy pasted this list to a separate *.py module and there it works fine… Tried to turn qs to iterator -same results.

in separate module

a = [93, 93, 93, 93, 93, 93, 93, 100, 102, 102, 102]

for i in a:
    if a.count(i) > 3:
        a.remove(i)
print(a)

----- >[93, 93, 93, 100, 102, 102, 102]

Upvotes: 0

Views: 94

Answers (1)

gachdavit
gachdavit

Reputation: 1261

Nothing is wrong with django here.

memory_limiter = BoatImage.objects.filter(boat_id__isnull=True).exclude(
    memory__in=existing_boats_pk).values_list("memory", flat=True) # This returns QuerySet object.

for i in memory_limiter:
    # QuerySet class has instance method .count(), but you can not provide parameters. Also, QuerySet does not support remove() method.
    # if memory_limiter.count(i)  >  3:
    print(memory_limiter.count())

Your code works on list. But Django's QuerySet and python's list are different objects, with different methods.

But you can do something like this. This should work(IMHO).

memory_limiter = list(BoatImage.objects.filter(boat_id__isnull=True).exclude(
        memory__in=existing_boats_pk).values_list("memory", flat=True)) # You should cast QuerySet object into list, then you can operate over it as a normal python's list.
for i in memory_limiter:
    if memory_limiter.count(i)  >  3:
        memory_limiter.remove(i)

Upvotes: 2

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