Cookies are returned in a RequestsCookieJar, which acts like a dict but also offers a more complete interface, suitable for use over multiple domains or paths. Cookie jars can also be passed in to requests:
返回的Cookie存储在RequestsCookieJar中，其作用类似于dict，同时提供了一个更完整的接口，适合在多个域或路径上使用。Cookie jar也可以传递给请求：
Sometimes you’ll want to omit session-level keys from a dict parameter. To do this, you simply set that key’s value to `None` in the method-level parameter. It will automatically be omitted.
prepped.body = 'No, I want exactly this as the body.'
# do something with prepped.headers
del prepped.headers['Content-Type']
resp = s.send(prepped,
stream=stream,
verify=verify,
proxies=proxies,
cert=cert,
timeout=timeout
)
print(resp.status_code)
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However, the above code will lose some of the advantages of having a requests Session object. In particular, Session-level state such as cookies will not get applied to your request. To get a PreparedRequest with that state applied, replace the call to Request.prepare() with a call to Session.prepare_request(), like this:
由于你没有对Request对象执行任何特殊操作，因此您可以立即prepare它并修改PreparedRequest对象。然后将其与发送给requests.*或Session.*的其它参数一起发送。
然而，上述代码将失去使用requests Session对象的一些优点。特别是Session级别的状态，比如cookie将不会应用于你的请求。如果需要获取应用了那些状态的 PreparedRequest，替换 Request.prepare() 调用为Session.prepare_request()，像这样：
prepped.body = 'Seriously, send exactly these bytes.'
# do something with prepped.headers
prepped.headers['Keep-Dead'] = 'parrot'
resp = s.send(prepped,
stream=stream,
verify=verify,
proxies=proxies,
cert=cert,
timeout=timeout
)
print(resp.status_code)
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When you are using the prepared request flow, keep in mind that it does not take into account the environment. This can cause problems if you are using environment variables to change the behaviour of requests. For example: Self-signed SSL certificates specified in REQUESTS_CA_BUNDLE will not be taken into account. As a result an SSL: CERTIFICATE_VERIFY_FAILED is thrown. You can get around this behaviour by explicitly merging the environment settings into your session:
当你使用prepared request请求时，请记住它没有考虑环境。如果你正使用环境变量来更改请求的行为，这可能会导致问题。例如：在REQUESTS_CA_BUNDLE中指定的自签名SSL证书将不起作用，结果引发了SSL:CERTIFICATE_VERIFY_FAILED。你可以通过将环境设置显式合并到Session中来避免这种行为：
对于分块编码请求的响应，最好使用Response.iter_content()对数据进行迭代。在理想情况下，将在请求上设置stream=True，在这种情况下，可以通过使用值为None的chunk_size参数调用iter_content来逐块迭代。如果要设置块的最大大小，可以将chunk_size参数设置为任意目标大小整数。
POST 多个分部编码(Multipart-Encoded)文件
The requests team has made a specific choice to use whatever SSL version is default in the underlying library (urllib3). Normally this is fine, but from time to time, you might find yourself needing to connect to a service-endpoint that uses a version that isn’t compatible with the default.
You can use Transport Adapters for this by taking most of the existing implementation of HTTPAdapter, and adding a parameter ssl_version that gets passed-through to urllib3. We’ll make a Transport Adapter that instructs the library to use SSLv3:
默认情况下，requests选择使用底层urllib3库中默认的SSL版本。 通常情况下，这是可以的，但有时，您可能会发现自己需要连接到使用与默认版本不兼容的SSL版本的服务端。
为此，可以通过继承HTTPAdapter实现自定义传输适配器，
示例：编写一个适配器，指示库使用SSLv3：
import ssl
from urllib3.poolmanager import PoolManager
from requests.adapters import HTTPAdapter
class Ssl3HttpAdapter(HTTPAdapter):
""""Transport adapter" that allows us to use SSLv3."""