How to return this valid json data in Python?

Question

I tested using Python to translate a curl to get some data.

import requests
import json

username="abc"
password="123"
headers = {
    'Content-Type': 'application/json',
}
params = (
    ('version', '2017-05-01'),
)

data = '{"text":["This is message one."], "id":"en-es"}'
response = requests.post('https://somegateway.service/api/abc', headers=headers, params=params, data=data, auth=(username, password))
print(response.text)

The above works fine. It returns json data. It seems ["This is message one."] is a list. I want to use a variable that loads a file to replace this list. I tried:

with open(f,"r",encoding='utf-8') as fp:
    file_in_list=fp.read().splitlines()
    toStr=str(file_in_list)
    data = '{"text":'+toStr+', "id":"en-es"}'
    response = requests.post('https://somegateway.service/api/abc', headers=headers, params=params, data=data, auth=(username, password))
    print(response.text)

But it returned error below.

{
  "code" : 400,
  "error" : "Mapping error, invalid JSON"
}

Can you help? How can I have valid response.text?

Thanks.

update:

The content of f contains only five lines below:

This is message one.
this is 2.
this is three.
this is four.
this is five.

Answer 1

The reason your existing code fails is that str applied to a list of strings will only rarely give you valid JSON. They're not intended to do the same thing. JSON only allows double-quoted strings; Python allows both single- and double-quoted strings. And, unless your strings all happen to include ' characters, Python will render them with single quotes:

>>> print(["abc'def"]) # gives you valid JSON, but only by accident
["abc'def"]
>>> print(["abc"]) # does not give you valid JSON
['abc']

If you want to get the valid JSON encoding of a list of strings, don't try to trick str into giving you valid JSON by accident, just use the json module:

toStr = json.dumps(file_in_list)

---

But, even more simply, you shouldn't be trying to figure out how to construct JSON strings in the first place. Just create a dict and json.dumps the whole thing:

data = {"text": file_in_list, "id": "en-es"}
data_str = json.dumps(data)

Being able to do this is pretty much the whole point of JSON: it's a simple way to automatically serialize all of the types that are common to all the major scripting languages.

---

Or, even better, let requests do it for you by passing a json argument instead of a data argument:

data = {"text": file_in_list, "id": "en-es"}
response = requests.post('https://somegateway.service/api/abc', headers=headers, params=params, json=data, auth=(username, password))

This also automatically takes care of setting the Content-Type header to application/json for you. You weren't doing that—and, while many servers will accept your input without it, it's illegal, and some servers will not allow it.

---

For more details, see the section More complicated POST requests in the requests docs. But there really aren't many more details.

Answer 2

tldr;

toStr = json.dumps(file_in_list)

Explanation

Assuming your file contains something like String_A String_B

You need to ensure that toStr is:

1. Enclosed by [ and ]
2. Every String in the list is enclosed by quotation marks.

So your raw json (as a String) is equal to '{"text":["String_A", "String_B"], "id":"en-es"}'