Language characteristics

Why? c++ Than python fast ？

1.Python After more layers , Even numbers object.
2.Python It's the interpretation of execution , And physical machines CPU There is an interpreter layer between them , and C++ It's compiled , It's the machine code directly , The compiler can also perform some optimizations during compilation .

python Multithreading is pseudo multithreading

The interpreter provides GIL（ Global Interpreter Lock , Global interpreter lock ） Ensure thread data synchronization , Only one thread is executing at a time .

You can use multiple processes to achieve parallelism .

#  Multithreading 
from threading import Thread
def spawn_n_threads(n, target):
    threads = []
    for _ in range(n):
        thread = Thread(target=target)
        thread.start()
        threads.append(thread)
    for thread in threads:
        thread.join()

#  Multi process 
from multiprocessing import Process
def spawn_n_processes(n, target):
    threads = []
    for _ in range(n):
        thread = Process(target=target)
        thread.start()
        threads.append(thread)
    for thread in threads:
        thread.join()

python Decorator

In order to reuse the code and call the original function to realize the new function

#  Pass in a function , Returns a new decorated function 
def timer(func):
    def deco():
        print("add something 1")
        func()
        print("add something 2")
    return deco

#  use @ Symbol tell python,foo This function is timer Decorated , call foo Will call directly timer（foo）
@timer
def foo():
    print("1000lines")

foo()