CODEWITHSUNDEEP
pythonlistdictionary
Legion
Legion

Reputation: 474

How to change a list within a dictionary?

I've made a parser to extract questions from past exam papers and tabulate how often particular questions/topics arise through the years. It stores the question/topic as a dictionary and the date as a list and is supposed to combine both as follows:

questions = {'Question1':['April 2011', 'May 2016'], 'Question2': ['June 2013']}

Problem is, I'm unable to update the list of dates within the dictionary. A snippet of my code is as follows:

def extract_topics_dates(file):
corpus = ''
topics = []
questions = {}
year = []
pdf_reader = PyPDF2.PdfFileReader(open(file, 'rb'))
for page in pdf_reader.pages:
    #For each page, get corpus of text.
    for line in page.extractText().splitlines():
        corpus = corpus + line

    #For each page, extract topics.
    for i in [phrase for phrase in map(str.strip, re.split('\d+\s\s', corpus)) if phrase]:
        topics.append(extract_topic(i))
    topics = [x for x in topics if x is not None]

    #For each page, extract date. 
    year = set([x for x in year if x is not None])
    year.add(get_date(page))

    #For each page, now combine the topic + date.
    for i in topics:
        questions[i].add(year)

return questions

Everything in this function works as intended, except the last questions[i].add(year) which returns a KeyError. Where am I going wrong?

Upvotes: 1

Views: 52

Answers (1)

Anatolii
Anatolii

Reputation: 14660

You should create a list for your key in the dictionary before adding anything to it. Please change that for loop to the following:

for i in topics:
    if i not in questions:
        questions[i] = list()    
    questions[i].append(year)

Or, as suggested by @Jon Clements:

for topic in topics:
    questions.setdefault(topic, []).append(year)

Upvotes: 1

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