[Answered ]-Python is printing one list backwards but not the others

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2👍

✅

I’ll shorten the code to the specific part that was very likely the issue:

query = table.objects.values(genus, species)
valueList = []
for q in query:
    species = ' '.join(q.values())
    valueList.append(species)

As you read in the documentation, values() will return a list of dictionaries, like this:

[{'genus_hetr': 'foogenus', 'species_hetr': 'foospecie'},
 {'genus_hetr': 'bargenus', 'species_hetr': 'barspecie'}]

You would then iterate through that list. On each iteration, q is one of the dicionaries. So far so good. Then, the issue:

' '.join(q.values())

A dictionary has no ordering. So this would join all values alright, but in an arbitrary order. Even those table you thought were working would have broken randomly at a later point.

So how to fix that? Well, like you did, using values_list returns tuples, which are ordered. Another option would have been to not rely on the order, but use the dictionary as such, that is, addressing it by key:

species = '%s %s' % (q[genus], q[species])

By the way, for such a simple case you probably want to use a list comprehension. The whole loop can be written like this:

valuesList = ['%s %s' % (q[genus], q[species]) for q in query]
👤spectras

0👍

As the docs would have it, instead of returning a dictionary (that was back to front for that one table), there is an option to return a value list. This came out the right way round and so the queryBuilder() function works like this:

views.py

def queryBuilder(table, column_str):

genus = 'genus_' + column_str
species = 'species_' + column_str
filterSp = {species: 'sp.'}


query = table.objects.values_list(genus, species).distinct().exclude(**filterSp)
valueList = []
for q in sorted(query):
    species = ' '.join(q)
    valueList.append(species)

return(valueList)

I still don’t know why the previous query was coming out the wrong way around for that one table which is annoying.

👤Oliver Burdekin

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