python基础---->python的使用(五)

　　这里记录一些python的一些基础知识，主要内容是高阶函数的使用。或许我的心包有一层硬壳，能破壳而入的东西是极其有限的。所以我才不能对人一往情深。

python中的高阶函数

一、map()、reduce()和filter()函数使用

　　 map()函数接收两个参数，一个是函数，一个是Iterable，map将传入的函数依次作用到序列的每个元素，并把结果作为新的Iterator返回。

def f(x):
    return x * x
print(list(map(f, range(1, 7)))) # [1, 4, 9, 16, 25, 36]

print(list(map(lambda x: x * x, range(1, 7)))) # [1, 4, 9, 16, 25, 36]

　　 reduce把一个函数作用在一个序列[x1, x2, x3, ...]上，这个函数必须接收两个参数，reduce把结果继续和序列的下一个元素做累积计算。

from functools import reduce
def add(x, y):
    return x + y
print(reduce(add, range(1, 10))) # 45

print(reduce(lambda x, y: x + y, range(1, 10))) # 45

　　 filter()函数用于过滤序列。

def is_odd(n):
    return n % 2 == 0
print(list(filter(is_odd, range(1, 10)))) # [2, 4, 6, 8]

print(list(filter(lambda x: x % 2 == 0, range(1, 10)))) # [2, 4, 6, 8]

　　sorted()函数用于排序。

def ownSort(n):
    return str(abs(n))[0]

sortList = [-3, 9, -7, 10]
print(sorted(sortList)) # [-7, -3, 9, 10]
print(sorted(sortList, key=abs)) # [-3, -7, 9, 10]
print(sorted(sortList, key=abs, reverse=True)) # [10, 9, -7, -3]
print(sorted(sortList, key=ownSort)) # [10, -3, -7, 9]

二、关于python变量的作用域理解

def scope_test():
    def do_local():
        spam = "local spam"

    def do_nonlocal():
        nonlocal spam
        spam = "nonlocal spam"

    def do_global():
        global spam
        spam = "global spam"

    spam = "test spam"
    do_local()
    print("After local assignment:", spam)
    do_nonlocal()
    print("After nonlocal assignment:", spam)
    do_global()
    print("After global assignment:", spam)
    
scope_test()
print("In global scope:", spam)

# After local assignment: test spam
# After nonlocal assignment: nonlocal spam
# After global assignment: nonlocal spam
# In global scope: global spam

　　Note how the local assignment (which is default) didn’t change scope_test’s binding of spam. The nonlocal assignment changed scope_test’s binding of spam, and the global assignment changed the module-level binding.

三、python中协程的一个案例

import asyncio
import random
import threading

async def Hello(index):
    print('Hello world! index=%s, thread=%s' % (index, threading.currentThread()))
    await asyncio.sleep(random.randint(1, 5))
    print('Hello again! index=%s, thread=%s' % (index, threading.currentThread()))

loop = asyncio.get_event_loop()
tasks = [Hello(1), Hello(2)]
loop.run_until_complete(asyncio.wait(tasks))
loop.close()

运行的结果如下：

Hello world! index=2, thread=<_MainThread(MainThread, started 37900)>
Hello world! index=1, thread=<_MainThread(MainThread, started 37900)>
Hello again! index=1, thread=<_MainThread(MainThread, started 37900)>
Hello again! index=2, thread=<_MainThread(MainThread, started 37900)>

四、python中的base64编码与解码

import base64
# base64编码
m = base64.b64encode(b'my name is huhx.')
print(m) # b'bXkgbmFtZSBpcyBodWh4Lg=='

# # base64解码
bytes = base64.b64decode(m)
print(bytes) # b'my name is huhx.'

codecs模块的简单使用

print('中国'.encode('utf-8')) # b'xe4xb8xadxe5x9bxbd'
print('中国'.encode('gbk')) # b'xd6xd0xb9xfa'

import codecs
print(codecs.encode('中国', 'utf-8')) # b'xe4xb8xadxe5x9bxbd'
print(codecs.encode('中国', 'gbk')) # b'xd6xd0xb9xfa'

str对象的encode方法的文档如下：

def encode(self, encoding='utf-8', errors='strict'): # real signature unknown; restored from __doc__
    """
    S.encode(encoding='utf-8', errors='strict') -> bytes
    
    Encode S using the codec registered for encoding. Default encoding
    is 'utf-8'. errors may be given to set a different error
    handling scheme. Default is 'strict' meaning that encoding errors raise
    a UnicodeEncodeError. Other possible values are 'ignore', 'replace' and
    'xmlcharrefreplace' as well as any other name registered with
    codecs.register_error that can handle UnicodeEncodeErrors.
    """
    return b""

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