class FormatChange:
def __init__(self, x, y):
self.x = x
self.y = y

def __repr__(self):
return f'use repr method: ({self.x}, {self.y})'

def __str__(self):
return f'use str method: ({self.x}, {self.y})'
fc = FormatChange(5, 7)
print(fc.__repr__()) # use repr method: (5, 7)
print(fc) # use str method: (5, 7)
print(f'fc is {fc!r}') #!r表示用repr方法代替str方法輸出

format_dict = {
'ymd': '{d.year}-{d.month}-{d.day}',
'mdy': '{d.month}/{d.day}/{d.year}',
'dmy': '{d.day}/{d.month}/{d.year}'
}
class Date:
def __init__(self, year, month, day):
self.year = year
self.month = month
self.day = day

def __format__(self, format_type='ymd'):
#format_type: 格式化類型，默認使用 ymd 方式
if not format_type:
format_type = 'ymd'
fmt = format_dict[format_type]
return fmt.format(d=self)#這里的format是一個鉤子函數(shù)
curr_data = Date(2020, 5, 6)
#這處其實調(diào)用的format是一個類庫中的方法，然后反向調(diào)用了自定義覆寫的format方法
print(f'default format: {format(curr_data)}') #2020-5-6
print(f"use mdy format: {format(curr_data, 'mdy')}") #5/6/2020

class Date:
__slots__ = ['year', 'month', 'day']
def __init__(self, year, month, day):
self.year = year
self.month = month
self.day = day

import math
class Point:
def __init__(self, x, y):
self.x = x
self.y = y
def __repr__(self):
return f'Point({self.x!r:},{self.y!r:})'
def distance(self, x, y):
return math.hypot(self.x - x, self.y - y)
#第一種方式：這種方式感覺用處不是太大，前面還是得new一個對象
p = Point(2, 3)
d = getattr(p, 'distance')(0, 0)
import operator
operator.methodcaller('distance', 0, 0)(p)
#用相同的參數(shù)多次調(diào)用某個方法時
points = [
Point(1, 2),
Point(3, 0),
Point(10, -3),
Point(-5, -7),
Point(-1, 8),
Point(3, 2)
]
#第二種使用方法： Sort by distance from origin (0, 0)
points.sort(key=operator.methodcaller('distance', 0, 0))
p = Point(3, 4)
d = operator.methodcaller('distance', 0, 0)
print(f'd(p) = {d(p)}')#5.0

from socket import socket, AF_INET, SOCK_STREAM
class LazyConnection:
def __init__(self, address, family=AF_INET, type=SOCK_STREAM):
self.address = address
self.family = family
self.type = type
self.sock = None
def __enter__(self):
if self.sock is not None:
raise RuntimeError('Already connected')
self.sock = socket(self.family, self.type)
self.sock.connect(self.address)
return self.sock
def __exit__(self, exc_ty, exc_val, tb):
self.sock.close()
self.sock = None
from functools import partial
conn = LazyConnection(('www.python.org', 80))
# Connection closed
with conn as s:
# conn.__enter__() executes: connection open
s.send(b'GET /index.html HTTP/1.0\r\n')
s.send(b'Host: www.python.org\r\n')
s.send(b'\r\n')
resp = b''.join(iter(partial(s.recv, 8192), b''))