解决USDA ESMIS API的Bad Request错误——Python requests调用问题

Let's break down why your curl command works but your Python code doesn't, and fix it step by step.

The Root Cause #

When you use curl with -d '{"auth": {...}}' and set Content-Type: application/json, you're sending a raw JSON string as the request body. But in your original Python code, passing a dictionary to the data parameter tells Requests to encode it as application/x-www-form-urlencoded (form data) instead of JSON—even if you manually set the Content-Type header. The USDA API expects JSON, so it rejects the mismatched form data with a 400 error.

The Fix: Use the json Parameter #

Requests has a built-in json parameter that handles both serializing your dictionary to JSON and setting the correct Content-Type: application/json header automatically. Here's the corrected code:

import requests
import getpass

email = "r******@gmail.com"
password = getpass.getpass()

data = {"auth": {"email": email, "password": password}}
url = "https://usda.library.cornell.edu/user_token"

# Use the json parameter instead of data
response = requests.post(url, json=data)

print(f"Status Code: {response.status_code}")
# Check the actual error message from the server (critical for debugging!)
if response.status_code != 200:
    print("Server Error Message:", response.text)
else:
    print("Success! Token:", response.json())

If You Still Run Into Issues #

If you tried the json parameter and it didn't work, here are quick troubleshooting checks:

• Verify credentials: Temporarily print the data dictionary (don't commit this to code!) to make sure the email and password from getpass are correctly captured.
• Check for special characters: If your password has characters like &, =, or quotes, json ensures they're properly escaped in the request—something form encoding might mangle.
• Avoid conflicting headers: When using json, you don't need to manually set Content-Type—Requests does it for you. If you add the header anyway, double-check for typos (e.g., application/json is spelled correctly).

Alternative: Manual JSON Serialization #

If you prefer to use data (not recommended, but for completeness), you need to manually serialize the dictionary to a JSON string with json.dumps:

import json
import requests
import getpass

email = "r******@gmail.com"
password = getpass.getpass()

data = {"auth": {"email": email, "password": password}}
headers = {"Content-Type": "application/json"}
url = "https://usda.library.cornell.edu/user_token"

response = requests.post(url, data=json.dumps(data), headers=headers)

Always check response.text when you get a 400 error—it will usually tell you exactly what the server is missing or rejecting (e.g., "invalid JSON format" or "missing auth fields").

内容的提问来源于stack exchange，提问作者Rutger Hofste