functools: partial และ reduce

ภาพรวม functools

import functools

# partial, reduce, lru_cache, wraps, cached_property ...
print(dir(functools))

partial()

import functools

def power(base, exp):
    return base ** exp

square = functools.partial(power, exp=2)
cube   = functools.partial(power, exp=3)

print(square(4))  # 16
print(cube(3))    # 27

partial กับเมธอด

import functools, logging

logger = logging.getLogger("app")
log_error = functools.partial(logger.log, logging.ERROR)

log_error("Something went wrong")

partial เทียบกับ lambda

import functools

mul = lambda x, y: x * y

double_lambda = lambda x: mul(x, 2)            # lambda approach
double_partial = functools.partial(mul, y=2)   # partial approach

print(double_partial(5))   # 10

reduce()

import functools, operator

total = functools.reduce(operator.add, [1,2,3,4,5])
print(total)   # 15

product = functools.reduce(operator.mul, [1,2,3,4,5], 1)
print(product) # 120

การสร้าง max() ด้วย reduce

import functools

def my_max(seq):
    return functools.reduce(lambda a, b: a if a > b else b, seq)

print(my_max([3, 1, 4, 1, 5, 9]))  # 9

การคลี่รายการซ้อนกัน

import functools, operator

nested = [[1,2],[3,4],[5]]
flat = functools.reduce(operator.iconcat, nested, [])
print(flat)  # [1, 2, 3, 4, 5]

partial สำหรับการสร้าง URL

import functools, urllib.request

def fetch(base, path):
    url = base.rstrip("/") + "/" + path.lstrip("/")
    with urllib.request.urlopen(url) as r:
        return r.read()

github = functools.partial(fetch, "https://api.github.com")
# github("/users/octocat")

wraps(): การคงข้อมูลเมทาดาทา

import functools

def decorator(func):
    @functools.wraps(func)
    def wrapper(*args, **kw):
        return func(*args, **kw)
    return wrapper

@decorator
def greet(name):
    """Say hello."""
    return f"Hello, {name}"

print(greet.__name__)  # greet
print(greet.__doc__)   # Say hello.

total_ordering

import functools

@functools.total_ordering
class Version:
    def __init__(self, major, minor):
        self.v = (major, minor)
    def __eq__(self, o): return self.v == o.v
    def __lt__(self, o): return self.v < o.v

print(Version(1,2) >= Version(1,1))  # True

singledispatch

import functools

@functools.singledispatch
def process(arg):
    raise NotImplementedError(type(arg))

@process.register(int)
def _(n): return n * 2

@process.register(str)
def _(s): return s.upper()

print(process(5))     # 10
print(process("hi"))  # HI

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