Requests 从入门到精通

背景

HTTP 是互联网应用层最核心的协议。Requests 将这个协议中每次都需要处理的 headers、cookies、认证、超时等细节封装得极其优雅，让开发者专注于业务逻辑。

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第 1 章：HTTP 方法速览

import requests

# GET — 获取资源
r = requests.get("https://httpbin.org/get")

# POST — 创建资源
r = requests.post("https://httpbin.org/post", json={"name": "Alice"})
r = requests.post("https://httpbin.org/post", data={"name": "Alice"})  # form 编码

# PUT — 更新资源
r = requests.put("https://httpbin.org/put", data={"key": "value"})

# DELETE — 删除资源
r = requests.delete("https://httpbin.org/delete")

# HEAD — 只获取响应头
r = requests.head("https://httpbin.org/get")

# PATCH — 部分更新
r = requests.patch("https://httpbin.org/patch", data={"key": "value"})

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第 2 章：Session 与持久化连接

# Session 保持连接和 Cookie
s = requests.Session()
s.headers.update({"User-Agent": "MyApp/1.0"})
s.auth = ("username", "password")

# 共享连接池，自动管理 Cookie
login_resp = s.post("https://example.com/login", json={"user": "a", "pass": "b"})
dashboard = s.get("https://example.com/dashboard")

# Session 级别重试策略
from requests.adapters import HTTPAdapter
from urllib3.util.retry import Retry

retry = Retry(total=3, backoff_factor=0.5, status_forcelist=[500, 502, 503])
s.mount("https://", HTTPAdapter(max_retries=retry))

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第 3 章：文件上传与流式下载

# 上传文件
files = {"file": open("report.pdf", "rb")}
r = requests.post("https://httpbin.org/post", files=files)

# 流式下载大文件
with requests.get("https://example.com/large_file.zip", stream=True) as r:
    r.raise_for_status()
    with open("large_file.zip", "wb") as f:
        for chunk in r.iter_content(chunk_size=8192):
            f.write(chunk)

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第 4 章：认证方式

# Basic Auth
requests.get("https://api.example.com", auth=("user", "pass"))

# Bearer Token
headers = {"Authorization": "Bearer eyJhbGciOi..."}
requests.get("https://api.example.com", headers=headers)

# OAuth2 客户端凭证
from requests.auth import HTTPBasicAuth
auth = HTTPBasicAuth("client_id", "client_secret")
data = {"grant_type": "client_credentials"}
r = requests.post("https://auth.example.com/token", auth=auth, data=data)
token = r.json()["access_token"]

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第 5 章：异常处理与超时

try:
    r = requests.get("https://api.example.com", timeout=(3.0, 10.0))
    # timeout=(连接超时, 读取超时)
    r.raise_for_status()  # 非 2xx 抛出 HTTPError
except requests.exceptions.Timeout:
    print("请求超时")
except requests.exceptions.ConnectionError:
    print("连接失败，检查网络或 URL")
except requests.exceptions.HTTPError as e:
    print(f"HTTP 错误: {e}")
except requests.exceptions.RequestException as e:
    print(f"请求异常: {e}")

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思考题

1. Session 和直接调用 requests.get() 有什么区别？什么场景下必须使用 Session？
2. stream=True 下载时，iter_content 和 iter_lines 分别适合什么场景？
3. 如何为 Requests 添加自定义的 DNS 解析（如使用 DoH）？