Content-Length如何计算

我还没明白原理不过这代码可以实现 可以用 有时间再看原理

import requests
 
 
def get_content_length(data):
    length = len(data.keys()) * 2 - 1
    total = ''.join(list(data.keys()) + list(data.values()))
    length += len(total)
    return length
 
 
data ={}
data['search[city1]'] = '19'
data['search[city2]'] = '291'
data['search[city3]'] = '0'
data['b1']='查询'
req = requests.post('http://httpbin/post', data)

print('实际的Content-Length为', req.json()['headers']['Content-Length'])