Efficiently combining, counting, and iterating

Scrivere codice Python efficiente

Logan Thomas

Scientific Software Technical Trainer, Enthought

Pokémon Overview

Trainers (collect Pokémon)

alt=”Ash Ketchum; one of the many characters (called trainers) in the Nintendo video game Pokémon”

Pokémon Overview

Pokémon (fictional animal characters)

alt=”Squirtle, Pikachu, Bulbasaur, and Charmander; a few of the many Pokémon that exist in the Nintendo video game”

Pokémon Overview

Pokédex (stores captured Pokémon)

alt=”Pokédex, a tool used by trainers to store captured Pokémon”

Pokémon Description

alt=”The Pokémon named Squirtle along with its accompanying metadata”

Pokémon Description

alt=”The Pokémon named Squirtle along with its accompanying metadata and the Name and Generation field highlighted”

Pokémon Description

alt=”The Pokémon named Squirtle along with its accompanying metadata and the Type and Legendary field highlighted”

Pokémon Description

alt=”The Pokémon named Squirtle along with its accompanying metadata and the Health Points, Attack, Defense, Special Attack, Special Defense, Speed, and Total fields highlighted”

Combining objects

names = ['Bulbasaur', 'Charmander', 'Squirtle']
hps = [45, 39, 44]

combined = []

for i,pokemon in enumerate(names):
    combined.append((pokemon, hps[i]))

print(combined)

[('Bulbasaur', 45), ('Charmander', 39), ('Squirtle', 44)]

Combining objects with zip

names = ['Bulbasaur', 'Charmander', 'Squirtle']
hps = [45, 39, 44]

combined_zip = zip(names, hps)

print(type(combined_zip))

<class 'zip'>

combined_zip_list = [*combined_zip]

print(combined_zip_list)

[('Bulbasaur', 45), ('Charmander', 39), ('Squirtle', 44)]

The collections module

Part of Python's Standard Library (built-in module)
Specialized container datatypes
- Alternatives to general purpose dict, list, set, and tuple
Notable:
- namedtuple: tuple subclasses with named fields
- deque: list-like container with fast appends and pops
- Counter: dict for counting hashable objects
- OrderedDict: dict that retains order of entries
- defaultdict: dict that calls a factory function to supply missing values

The collections module

Part of Python's Standard Library (built-in module)
Specialized container datatypes
- Alternatives to general purpose dict, list, set, and tuple
Notable:
- namedtuple: tuple subclasses with named fields
- deque: list-like container with fast appends and pops
- Counter: dict for counting hashable objects
- OrderedDict: dict that retains order of entries
- defaultdict: dict that calls a factory function to supply missing values

Counting with loop

# Each Pokémon's type (720 total)
poke_types = ['Grass', 'Dark', 'Fire', 'Fire', ...]

type_counts = {}

for poke_type in poke_types:
    if poke_type not in type_counts:
        type_counts[poke_type] = 1
    else:
        type_counts[poke_type] += 1

print(type_counts)

{'Rock': 41, 'Dragon': 25, 'Ghost': 20, 'Ice': 23, 'Poison': 28, 'Grass': 64,
 'Flying': 2, 'Electric': 40, 'Fairy': 17, 'Steel': 21, 'Psychic': 46, 'Bug': 65,
 'Dark': 28, 'Fighting': 25, 'Ground': 30, 'Fire': 48,'Normal': 92, 'Water': 105}

collections.Counter()

# Each Pokémon's type (720 total)
poke_types = ['Grass', 'Dark', 'Fire', 'Fire', ...]

from collections import Counter

type_counts = Counter(poke_types)

print(type_counts)

Counter({'Water': 105, 'Normal': 92, 'Bug': 65, 'Grass': 64, 'Fire': 48,
         'Psychic': 46, 'Rock': 41, 'Electric': 40, 'Ground': 30,
         'Poison': 28, 'Dark': 28, 'Dragon': 25, 'Fighting': 25, 'Ice': 23,
         'Steel': 21, 'Ghost': 20, 'Fairy': 17, 'Flying': 2})

The itertools module

Part of Python's Standard Library (built-in module)
Functional tools for creating and using iterators
Notable:
- Infinite iterators: count, cycle, repeat
- Finite iterators: accumulate, chain, zip_longest, etc.
- Combination generators: product, permutations, combinations

The itertools module

Part of Python's Standard Library (built-in module)
Functional tools for creating and using iterators
Notable:
- Infinite iterators: count, cycle, repeat
- Finite iterators: accumulate, chain, zip_longest, etc.
- Combination generators: product, permutations, combinations

Combinations with loop

poke_types = ['Bug', 'Fire', 'Ghost', 'Grass', 'Water']

combos = []

for x in poke_types:
    for y in poke_types:
        if x == y:
            continue
        if ((x,y) not in combos) & ((y,x) not in combos):
            combos.append((x,y))

print(combos)

[('Bug', 'Fire'), ('Bug', 'Ghost'), ('Bug', 'Grass'), ('Bug', 'Water'),
 ('Fire', 'Ghost'), ('Fire', 'Grass'), ('Fire', 'Water'),
 ('Ghost', 'Grass'), ('Ghost', 'Water'), ('Grass', 'Water')]

itertools.combinations()

poke_types = ['Bug', 'Fire', 'Ghost', 'Grass', 'Water']

from itertools import combinations

combos_obj = combinations(poke_types, 2)

print(type(combos_obj))

<class 'itertools.combinations'>

combos = [*combos_obj]
print(combos)

[('Bug', 'Fire'), ('Bug', 'Ghost'), ('Bug', 'Grass'), ('Bug', 'Water'),
 ('Fire', 'Ghost'), ('Fire', 'Grass'), ('Fire', 'Water'),
 ('Ghost', 'Grass'), ('Ghost', 'Water'), ('Grass', 'Water')]

Let's practice!

Scrivere codice Python efficiente