Insert and Updating Dictionaries

#python #datastructure #programming #language #O1

There is some to insert elements and update them in using dict in Python
We can use setdefault to set a default value when a key does not exist.

import re
import sys
WORD_RE = re.compile(r'\w+')
index = {}
with open(sys.argv[1], encoding='utf-8') as fp:
    for line_no, line in enumerate(fp, 1):
        for match in WORD_RE.finditer(line):
            word = match.group()
            column_no = match.start() + 1
            location = (line_no, column_no)
            index.setdefault(word, []).append(location)
# display in alphabetical order
for word in sorted(index, key=str.upper):
    print(word, index[word])

The following piece of code means index.setdefault(word, []).append(location):

if key not in my_dict:
    my_dict[key] = []
my_dict[key].append(new_value)

The code above in other words, if a key does not exist put an empty list there, if exists append a value on the list
It is possible to use defauldict as well
defaultdict uses a default_factory to fill the key.

index = collections.defaultdict(list) # Fill the key with a empty list
with open(sys.argv[1], encoding='utf-8') as fp:
    for line_no, line in enumerate(fp, 1):
        for match in WORD_RE.finditer(line):
            word = match.group()
            column_no = match.start() + 1
            location = (line_no, column_no)

How to handle missing on dictionary

References

Ramalho, 2022, 83-96