# Iterate over a list of list names as file names

Interrogating a web API using query-url's, for each query I can get either zero hits, one hit, or multiple hits. Each of those categories needs to go into a separate CSV file for manual review or processing later. (More on this project here and here).

The input data (from a 14K line csv, one line per artist) is full of holes. Only a name is always given, but may be misspelled or in a form that the API does not recognise. Birth dates, death dates may or may not be known, with a precision like for example 'not before may 1533, not after january 1534'. It may also have exact dates in ISO format.

Using those three different output csv's, the user may go back to their source, try to refine their data, and run the script again to get a better match. Exactly one hit is what we go for: a persistent identifier for this specific artist.

In the code below, df is a Pandas dataframe that has all the information in a form that is easiest to interrogate the API with.

First, I try to get an exact match best_q (exact match of name string + any of the available input fields elsewhere in the record), if that yields zero, I try a slightly more loose match bracket_q (any of the words in the literal name string + any of the available input fields elsewhere in the record).

I output the dataframe as a separate csv, and each list of zero hits, single hits, or multiple hits also in a separate csv.

I'm seeking advice on two specific things.

1. Is there a more Pythonic way of handling the lists? Right now, I think the code is readable enough, but I have one line to generate the lists, another to put them in a list of lists, and another to put them in a list of listnames.

2. The second thing is the nested if..elif on zero hits for the first query. I know it ain't pretty, but it's still quite readable (to me), and I don't see how I could do that any other way. That is: I have to try best q first, and only if it yields zero, try again with bracket_q.

I have omitted what goes before. It works, it's been reviewed, I'm happy with it.

A final note: I'm not very concerned about performance, because the API is the bottleneck. I am concerned about readability. Users may want to tweak the script, somewhere down the line.

singles, multiples, zeroes = ([] for i in range(3))

for row in df.itertuples():
query = best_q(row)
if hits == 1:
singles.append([row.priref, row.name, hits, uri])
elif hits > 1:
multiples.append([row.priref, row.name, hits])
elif hits == 0:
query = bracket_q(row)
if hits == 1:
singles.append([row.priref, row.name, hits, uri])
elif hits > 1:
multiples.append([row.priref, row.name, hits])
elif hits == 0:
zeroes.append([row.priref, str(row.name)])  # PM: str!!

lists = singles, multiples, zeroes
listnames = ['singles','multiples','zeroes']

for s, l in zip(listnames, lists):
listfile = '{}_{}.csv'.format(input_fname, s)
writelist(list=l, fname=listfile)

outfile = fname + '_out' + ext
df.to_csv(outfile, sep='|', encoding='utf-8-sig')


As you already noticed you have repeated code. you have variable names for your lists and also string definitions for list names which most probably should match. while this is no big problem for just 3 lists it could get cumbersome on adding another list. A simple way to avoid such name-to-string matching edits is to hold such variables in a dict() and have the string definition only.

The second problem is to have different iterables which must match in length and order to be zipped lateron. Avoid this by holding tuples (or other containers) in a single iterable from the beginning. key-value pairs in a dict() also provide this binding.

I your case I'd recommend to use the strings as keys

#avoid named variables
lists = {name:[] for name in ('singles', 'multiples' , 'zeros')}

#access lists via name
lists['singles'].append(0)

#access via temporary
l = lists['singles']
l.append[0]

#iterate for saving
for s, l in lists.items():
writelist(list=l, fname=s + '.csv')


EDIT:

Above answer applies to the first version of code where all that list init was skipped. While all still valid this can now be applied to the real code. concise and following the KISS principle. Names could be improved but are left here for outlining changes only.

lists = {name:[] for name in ('singles', 'multiples' , 'zeros')}

for row in df.itertuples():
query = best_q(row)
if hits == 0:
query = bracket_q(row)

if hits == 1:
lists['singles'].append([row.priref, row.name, hits, uri])
elif hits > 1:
lists['multiples'].append([row.priref, row.name, hits])
elif hits == 0:
lists['zeroes'].append([row.priref, str(row.name)])  # PM: str!!

for s, l in lists.items():
listfile = '{}_{}.csv'.format(input_fname, s)
writelist(list=l, fname=listfile)

outfile = fname + '_out' + ext
df.to_csv(outfile, sep='|', encoding='utf-8-sig')

1. You can simplify your if structure. You duplicate the code for hits == 1 and hits > 1. To do this move the if hits == 0 code into a 'guard-statement' that updates the state to the correct one.
2. You should create a class to help ease your use code. A simple class with an internal list, a name, a selection and a size would allow you to Significantly reduce the amount of code you'd have to write.
3. All the appends are the same, except you perform a slice to get the size that you'd like, you can do this in the list class made in 2.
4. You only change what list you append to in your ifs, and so you can use a dictionary to reduce the amount of code needed for this. You'd need to have a 'default' list and to use a dict.get.
5. You won't need to use zip if you make the list contain the name, leaving a basic for.

I don't really know what the rest of your functions are, and so I'll leave it at this:

class List(list):
def __init__(self, name, selection, size):
super().__init__()
self.name = name
self.selection = selection
self.size = size

self.append(value[:self.size])

lists = [
List('zeroes', 0, 2),
List('single', 1, 4),
List('multiples', None, 3),
]
list_selections = {l.selection: l for l in lists}
default = list_selections.pop(None)

for row in df.itertuples():
if hits == 0:

• Just so I remember later: the reason for the default is that it solves 'NoneType' object has no attribute 'add' when selection is None – RolfBly Aug 11 '18 at 9:40