0.爬虫 urlib库讲解 urlopen()与Request()

# 注意一下 是import urllib.request 还是 form urllib import request

0. urlopen()

语法：urllib.request.urlopen(url, data=None, [timeout, ]*, cafile=None, capath=None, cadefault=False, context=None)

• 实例0：(这个函数 一般就使用三个参数 url data timeout)

*添加的data参数需要使用bytes()方法将参数转换为字节流（区别于str的一种类型 是一种比特流 010010010）编码的格式的内容，即bytes类型。

*response.read()是bytes类型的数据，需要decode（解码）一下。

import urllib.parse
import urllib.request
import urllib.error
 
url = 'http://httpbin.org/post'
data = bytes(urllib.parse.urlencode({'word': 'hello'}), encoding='utf8')
try:
    response = urllib.request.urlopen(url, data=data,timeout=1)
except urllib.error.URLError as e:
    if isinstance(e.reason, socket.timeout):
        print('TIME OUT')
else:
    print(response.read().decode("utf-8"))

输出结果：

{
  "args": {},
  "data": "",
  "files": {},
  "form": {
    "word": "hello"
  },
  "headers": {
    "Accept-Encoding": "identity",
    "Content-Length": "10",
    "Content-Type": "application/x-www-form-urlencoded",
    "Host": "httpbin.org",
    "User-Agent": "Python-urllib/3.6"
  },
  "json": null,
  "origin": "101.206.170.234, 101.206.170.234",
  "url": "https://httpbin.org/post"
}

• 实例1：查看i状态码、响应头、响应头里server字段的信息

import urllib.request
 
response = urllib.request.urlopen('https://www.python.org')
print(response.status)
print(response.getheaders())
print(response.getheader('Server'))

输出结果：

200
[('Server', 'nginx'), ('Content-Type', 'text/html; charset=utf-8'), ('X-Frame-Options', 'DENY'), ('Via', '1.1 vegur'), ('Via', '1.1 varnish'), ('Content-Length', '48410'), ('Accept-Ranges', 'bytes'), ('Date', 'Tue, 09 Apr 2019 02:32:34 GMT'), ('Via', '1.1 varnish'), ('Age', '722'), ('Connection', 'close'), ('X-Served-By', 'cache-iad2126-IAD, cache-hnd18751-HND'), ('X-Cache', 'MISS, HIT'), ('X-Cache-Hits', '0, 1223'), ('X-Timer', 'S1554777154.210361,VS0,VE0'), ('Vary', 'Cookie'), ('Strict-Transport-Security', 'max-age=63072000; includeSubDomains')]
nginx

使用urllib库的urlopen()方法有很大的局限性，比如不能设置响应头的信息等。所以需要引入request()方法。

1. Request()

• 实例0：（这两种方法的实现效果是一样的）

import urllib.request
 
response = urllib.request.urlopen('https://www.python.org')
print(response.read().decode('utf-8'))
 
######################################
 
import urllib.request
 
req = urllib.request.Request('https://python.org')
response = urllib.request.urlopen(req)
print(response.read().decode('utf-8'))

下面主要讲解下使用Request()方法来实现get请求和post请求,并设置参数。

• 实例1：(post请求)

from urllib import request, parse
 
url = 'http://httpbin.org/post'
headers = {
    'User-Agent': 'Mozilla/4.0 (compatible; MSIE 5.5; Windows NT)',
    'Host': 'httpbin.org'
}
dict = {
    'name': 'Germey'
}
data = bytes(parse.urlencode(dict), encoding='utf8')
req = request.Request(url=url, data=data, headers=headers, method='POST')
response = request.urlopen(req)
print(response.read().decode('utf-8'))

亦可使用add_header()方法来添加报头，实现浏览器的模拟，添加data属性亦可如下书写：

补充：还可以使用bulid_opener()修改报头，不过多阐述，够用了就好。

from urllib import request, parse
 
url = 'http://httpbin.org/post'
dict = {
    'name': 'Germey'
}
data = parse.urlencode(dict).encode('utf-8')
req = request.Request(url=url, data=data, method='POST')
req.add_header('User-Agent', 'Mozilla/4.0 (compatible; MSIE 5.5; Windows NT)')
response = request.urlopen(req)
print(response.read().decode('utf-8'))

• 实例2：(get请求) 百度关键字的查询

from urllib import request,parse
 
url = 'http://www.baidu.com/s?wd='
key = '路飞'
key_code = parse.quote(key)
url_all = url + key_code
"""
#第二种写法
url = 'http://www.baidu.com/s'
key = '路飞'
wd = parse.urlencode({'wd':key})
url_all = url + '?' + wd
"""
req = request.Request(url_all)
response = request.urlopen(req)
print(response.read().decode('utf-8'))

在这里，对编码decode、reqest模块里的quote()方法、urlencode()方法 等就有疑问了，，对此，做一些说明：

1. parse.quote：将str数据转换为对应的编码
2. parse.urlencode：将字典中的k:v转换为K:编码后的v
3. parse.unquote：将编码后的数据转化为编码前的数据
4. decode 字符串解码 decode("utf-8")跟read()搭配很配！
5. encode 字符串编码

>>> str0 = '我爱你'
>>> str1 = str0.encode('gb2312')
>>> str1
b'\xce\xd2\xb0\xae\xc4\xe3'
>>> str2 = str0.encode('gbk')
>>> str2
b'\xce\xd2\xb0\xae\xc4\xe3'
>>> str3 = str0.encode('utf-8')
>>> str3
b'\xe6\x88\x91\xe7\x88\xb1\xe4\xbd\xa0'
>>> str00 = str1.decode('gb2312')
>>> str00
'我爱你'
>>> str11 = str1.decode('utf-8') #报错，因为str1是gb2312编码的
Traceback (most recent call last):
  File "<pyshell#9>", line 1, in <module>
    str11 = str1.decode('utf-8')
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xce in position 0: invalid continuation byte

* encoding指定编码格式

在这里，又有疑问了？read()、readline()、readlines()的区别：

1. read():全部，字符串str
2. reasline():一行
3. readlines():全部，列表list