Posts
Python高级语法
pre
Read The Fucking Source Code.
A picture is worth a thousand words
MISC
asterisk （*）
基础
传参
*args表示*args enable us to pass the variable number of non-keyword arguments to functions, but we cannot use this to pass keyword arguments. Keyword arguments mean that they contain a key-value pair, like a Python dictionary.
**kwargsallows us to pass any number of keyword arguments.
修饰器
举个例子：
def hello_decorator(func):
def inner1(*args, **kwargs):
print("before Execution")
# getting the returned value
returned_value = func(*args, **kwargs)
print("after Execution")
# returning the value to the original frame
return returned_value
return inner1
# adding decorator to the function
@hello_decorator
def sum_two_numbers(a, b):
print("Inside the function")
return a + b
a, b = 1, 2
# getting the value through return of the function
print("Sum =", sum_two_numbers(a, b))
Output:
before Execution
Inside the function
after Execution
Sum = 3
chain decorators
# code for testing decorator chaining
def decor1(func):
def inner():
x = func()
return x * x
return inner
def decor(func):
def inner():
x = func()
return 2 * x
return inner
@decor1
@decor
def num():
return 10
@decor
@decor1
def num2():
return 10
print(num())
print(num2())
Output:
400
200
协程
一系列api来执行并行任务，给出一些区别。
协程
import asyncio
async def main():
print('hello')
await asyncio.sleep(1)
print('world')
asyncio.run(main())
hello
world
注意：简单地调用一个协程并不会使其被调度执行
main()
<coroutine object main at 0x1053bb7c8>
可等待对象
可等待 对象有三种主要类型: 协程, 任务 和 Future.
协程
import asyncio
async def nested():
return 42
async def main():
# Nothing happens if we just call "nested()".
# A coroutine object is created but not awaited,
# so it *won't run at all*.
nested()
# Let's do it differently now and await it:
print(await nested()) # will print "42".
asyncio.run(main())
任务
import asyncio
async def nested():
return 42
async def main():
# Schedule nested() to run soon concurrently
# with "main()".
task = asyncio.create_task(nested())
# "task" can now be used to cancel "nested()", or
# can simply be awaited to wait until it is complete:
await task
asyncio.run(main())
Futures
import asyncio
async def main():
await function_that_returns_a_future_object()
# this is also valid:
await asyncio.gather(
function_that_returns_a_future_object(),
some_python_coroutine()
)
一个很好的返回对象的低层级函数的示例是 loop.run_in_executor()。