requests库是python爬虫使用频率最高的库，在网络请求中发挥着重要的作用，这边文章浅析requests的ＡＰＩ源码。
该库文件结构如图：
提供的核心接口在__init__文件中，如下：
from . import utils from . import packages from .models import Request, Response, PreparedRequest from .api import request, get, head, post, patch, put, delete, options from .sessions import session, Session from .status_codes import codes from .exceptions import ( RequestException, Timeout, URLRequired, TooManyRedirects, HTTPError, ConnectionError, FileModeWarning, ConnectTimeout, ReadTimeout )
ｒｅｑｕｅｓｔｓ常用方法在api.py文件中，源码如下：
# -*- coding: utf-8 -*- """ requests.api ~~~~~~~~~~~~ This module implements the Requests API. :copyright: (c) 2012 by Kenneth Reitz. :license: Apache2, see LICENSE for more details. """ from . import sessions def request(method, url, **kwargs): """Constructs and sends a :class:`Request <Request>`. :param method: method for the new :class:`Request` object. :param url: URL for the new :class:`Request` object. :param params: (optional) Dictionary, list of tuples or bytes to send in the body of the :class:`Request`. :param data: (optional) Dictionary, list of tuples, bytes, or file-like object to send in the body of the :class:`Request`. :param json: (optional) A JSON serializable Python object to send in the body of the :class:`Request`. :param headers: (optional) Dictionary of HTTP Headers to send with the :class:`Request`. :param cookies: (optional) Dict or CookieJar object to send with the :class:`Request`. :param files: (optional) Dictionary of ``'name': file-like-objects`` (or ``{'name': file-tuple}``) for multipart encoding upload. ``file-tuple`` can be a 2-tuple ``('filename', fileobj)``, 3-tuple ``('filename', fileobj, 'content_type')`` or a 4-tuple ``('filename', fileobj, 'content_type', custom_headers)``, where ``'content-type'`` is a string defining the content type of the given file and ``custom_headers`` a dict-like object containing additional headers to add for the file. :param auth: (optional) Auth tuple to enable Basic/Digest/Custom HTTP Auth. :param timeout: (optional) How many seconds to wait for the server to send data before giving up, as a float, or a :ref:`(connect timeout, read timeout) <timeouts>` tuple. :type timeout: float or tuple :param allow_redirects: (optional) Boolean. Enable/disable GET/OPTIONS/POST/PUT/PATCH/DELETE/HEAD redirection. Defaults to ``True``. :type allow_redirects: bool :param proxies: (optional) Dictionary mapping protocol to the URL of the proxy. :param verify: (optional) Either a boolean, in which case it controls whether we verify the server's TLS certificate, or a string, in which case it must be a path to a CA bundle to use. Defaults to ``True``. :param stream: (optional) if ``False``, the response content will be immediately downloaded. :param cert: (optional) if String, path to ssl client cert file (.pem). If Tuple, ('cert', 'key') pair. :return: :class:`Response <Response>` object :rtype: requests.Response Usage:: >>> import requests >>> req = requests.request('GET', 'https://httpbin.org/get') <Response [200]> """ # By using the 'with' statement we are sure the session is closed, thus we # avoid leaving sockets open which can trigger a ResourceWarning in some # cases, and look like a memory leak in others. with sessions.Session() as session: return session.request(method=method, url=url, **kwargs) def get(url, params=None, **kwargs): r"""Sends a GET request. :param url: URL for the new :class:`Request` object. :param params: (optional) Dictionary, list of tuples or bytes to send in the body of the :class:`Request`. :param \*\*kwargs: Optional arguments that ``request`` takes. :return: :class:`Response <Response>` object :rtype: requests.Response """ kwargs.setdefault('allow_redirects', True) return request('get', url, params=params, **kwargs) def options(url, **kwargs): r"""Sends an OPTIONS request. :param url: URL for the new :class:`Request` object. :param \*\*kwargs: Optional arguments that ``request`` takes. :return: :class:`Response <Response>` object :rtype: requests.Response """ kwargs.setdefault('allow_redirects', True) return request('options', url, **kwargs) def head(url, **kwargs): r"""Sends a HEAD request. :param url: URL for the new :class:`Request` object. :param \*\*kwargs: Optional arguments that ``request`` takes. :return: :class:`Response <Response>` object :rtype: requests.Response """ kwargs.setdefault('allow_redirects', False) return request('head', url, **kwargs) def post(url, data=None, json=None, **kwargs): r"""Sends a POST request. :param url: URL for the new :class:`Request` object. :param data: (optional) Dictionary, list of tuples, bytes, or file-like object to send in the body of the :class:`Request`. :param json: (optional) json data to send in the body of the :class:`Request`. :param \*\*kwargs: Optional arguments that ``request`` takes. :return: :class:`Response <Response>` object :rtype: requests.Response """ return request('post', url, data=data, json=json, **kwargs) def put(url, data=None, **kwargs): r"""Sends a PUT request. :param url: URL for the new :class:`Request` object. :param data: (optional) Dictionary, list of tuples, bytes, or file-like object to send in the body of the :class:`Request`. :param json: (optional) json data to send in the body of the :class:`Request`. :param \*\*kwargs: Optional arguments that ``request`` takes. :return: :class:`Response <Response>` object :rtype: requests.Response """ return request('put', url, data=data, **kwargs) def patch(url, data=None, **kwargs): r"""Sends a PATCH request. :param url: URL for the new :class:`Request` object. :param data: (optional) Dictionary, list of tuples, bytes, or file-like object to send in the body of the :class:`Request`. :param json: (optional) json data to send in the body of the :class:`Request`. :param \*\*kwargs: Optional arguments that ``request`` takes. :return: :class:`Response <Response>` object :rtype: requests.Response """ return request('patch', url, data=data, **kwargs) def delete(url, **kwargs): r"""Sends a DELETE request. :param url: URL for the new :class:`Request` object. :param \*\*kwargs: Optional arguments that ``request`` takes. :return: :class:`Response <Response>` object :rtype: requests.Response """ return request('delete', url, **kwargs)
常用的get、post、put、optins、delete方法都在该文件中实现，这些方法都是使用内部封装的一个模块：request，而request是对session.request内部模块的封装，提供一个上下文管理。
继续看最为核心的session.request模块源码:
def request(self, method, url, ······· # Create the Request. req = Request( method=method.upper(), url=url, headers=headers, files=files, data=data or {}, json=json, params=params or {}, auth=auth, cookies=cookies, hooks=hooks, ) prep = self.prepare_request(req) proxies = proxies or {} settings = self.merge_environment_settings( prep.url, proxies, stream, verify, cert ) # Send the request. send_kwargs = { 'timeout': timeout, 'allow_redirects': allow_redirects, } send_kwargs.update(settings) resp = self.send(prep, **send_kwargs) return resp
在这里提交过来的请求信息将组装成Request请求对象，并对其中的配置参数进行合并，然后将Request请求和配置参数发送给self.send，来请求下载，继续看self.send
def send(self, request, **kwargs): """Send a given PreparedRequest. :rtype: requests.Response """ # Set defaults that the hooks can utilize to ensure they always have # the correct parameters to reproduce the previous request. kwargs.setdefault('stream', self.stream) kwargs.setdefault('verify', self.verify) kwargs.setdefault('cert', self.cert) kwargs.setdefault('proxies', self.proxies) # It's possible that users might accidentally send a Request object. # Guard against that specific failure case. if isinstance(request, Request): raise ValueError('You can only send PreparedRequests.') # Set up variables needed for resolve_redirects and dispatching of hooks allow_redirects = kwargs.pop('allow_redirects', True) stream = kwargs.get('stream') hooks = request.hooks # Get the appropriate adapter to use adapter = self.get_adapter(url=request.url) # Start time (approximately) of the request start = preferred_clock() # Send the request r = adapter.send(request, **kwargs) # Total elapsed time of the request (approximately) elapsed = preferred_clock() - start r.elapsed = timedelta(seconds=elapsed) # Response manipulation hooks r = dispatch_hook('response', hooks, r, **kwargs) # Persist cookies if r.history: # If the hooks create history then we want those cookies too for resp in r.history: extract_cookies_to_jar(self.cookies, resp.request, resp.raw) extract_cookies_to_jar(self.cookies, request, r.raw) # Redirect resolving generator. gen = self.resolve_redirects(r, request, **kwargs) # Resolve redirects if allowed. history = [resp for resp in gen] if allow_redirects else [] # Shuffle things around if there's history. if history: # Insert the first (original) request at the start history.insert(0, r) # Get the last request made r = history.pop() r.history = history # If redirects aren't being followed, store the response on the Request for Response.next(). if not allow_redirects: try: r._next = next(self.resolve_redirects(r, request, yield_requests=True, **kwargs)) except StopIteration: pass if not stream: r.content return r
当然在self.send中核心的是下面几行行代码：
# Start time (approximately) of the request start = preferred_clock() # Send the request r = adapter.send(request, **kwargs) # Total elapsed time of the request (approximately) elapsed = preferred_clock() - start r.elapsed = timedelta(seconds=elapsed) # Response manipulation hooks r = dispatch_hook('response', hooks, r, **kwargs)
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分别进行请求，并将请求响应内容构造成响应对象r,其中又引入本地模块adapter，该模块主要负责请求处理及其响应内容。
requests库实现很巧妙，对cookie保持、代理问题、SSL验证问题都做了处理，功能很全，其中细节不仔细去研读很难理解，这里只是对其实现过程做一个浅析，如果有感兴趣的同学，可以仔细研读每个模块和功能，其中有奥妙。