Dictionary in python

#python #code #datastructure #performance

Unpacking dictionary 

>>> def dump(**kwargs):
...     return kwargs
...
>>> dump(**{'x': 1}, y=2, **{'z': 3})
{'x': 1, 'y': 2, 'z': 3}

Joining mapping 

>>> d1 = {'a': 1, 'b': 3}
>>> d2 = {'a': 2, 'b': 4, 'c': 6}
>>> d1 | d2
{'a': 2, 'b': 4, 'c': 6}

Userdict

  • UserDict is the best class to be inherent to create a custom dictionary class with some already implemented special functions. The keys need to be hashable (has hash code that never change between it life cycle)

setdefault

  • setdefault puts a default value when a key is not found in dictionary 
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)

for word in sorted(index, key=str.upper):
    print(word, index[word])

defauldict

  • Similar to setdefault, defaultdict put a default value as well. 
WORD_RE = re.compile(r'\w+')
index = collections.defaultdict(list)     # (1)
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[word].append(location)  # (2)

# display in alphabetical order
for word in sorted(index, key=str.upper):
    print(word, index[word])

[[]]❌

Special methods

  • __missing__, __eq__ and __hash__ are methods important to be implemented when inherent UserDict or dict
Eu com algumas figuras que representa análise de dados/ciência
#python #code #datastructure #performance