使用Python实现HTTP请求的三种方式（urllib模块、urllib3模块、requests模块），每种方式采用get和post两种请求模式，给出代码

在Python中，有几种常用的库用于发送HTTP请求，包括内置的`urllib`, `urllib3`, 和第三方库`requests`。这里我会分别演示如何使用这三种库来进行GET和POST请求：

1. **使用urllib模块** (基础版):

   import urllib.request

   # GET请求
   response_get = urllib.request.urlopen('http://example.com/api')
   data_get = response_get.read().decode()
   
   # POST请求 (使用urlencode)
   from urllib.parse import urlencode
   post_data = {'key': 'value'}
   post_urlencoded = urlencode(post_data)
   req_post = urllib.request.Request('http://example.com/api', post_urlencoded.encode())
   with urllib.request.urlopen(req_post) as response_post:
       post_data_response = response_post.read().decode()

2. **使用urllib3模块** (更高级，支持连接池等优化):

   import urllib3
   http = urllib3.PoolManager()

   # GET请求
   response_get = http.request('GET', 'http://example.com/api')
   data_get = response_get.data.decode()

   # POST请求
   post_data = {
       'key': 'value'
   }
   headers = {'Content-Type': 'application/x-www-form-urlencoded'}
   response_post = http.request('POST', 'http://example.com/api', fields=post_data, headers=headers)
   post_data_response = response_post.data.decode()

3. **使用requests模块** (最常用，功能强大且易用):

   import requests

   # GET请求
   response_get = requests.get('http://example.com/api')
   data_get = response_get.text

   # POST请求
   post_data = {'key': 'value'}
   response_post = requests.post('http://example.com/api', data=post_data)
   post_data_response = response_post.text