Graphic API upload to a certain library folder

I'm trying to upload an image from my local machine to the Qualtrics library. The cURL works fine, but the python request does not. Can anyone tell me the cause of the issue?

The CURL code
curl --request POST \\
 --url https://iad1.qualtrics.com/API/v3/libraries/libraryID/graphics \\
 --header 'Content-Type: multipart/form-data; boundary=---011000010111000001101001' \\
 --header 'X-API-TOKEN: tokenID' \\
 --form file=@/Users/username/Desktop/pic_1.png \\
 --form folder=foldername

The python code

conn = http.client.HTTPSConnection("iad1.qualtrics.com")
payload = "-----011000010111000001101001\\r\\nContent-Disposition: form-data; name=\\"name\\"\\r\\n\\r\\npic1.png\\r\\n-----011000010111000001101001\\r\\nContent-Disposition: form-data; name=\\"file\\"\\r\\n\\r\\n@/Users/username/Desktop/pic_1.png\\r\\n-----011000010111000001101001\\r\\nContent-Disposition: form-data; name=\\"contentType\\"\\r\\n\\r\\nimage/png\\r\\n-----011000010111000001101001\\r\\nContent-Disposition: form-data; name=\\"folder\\"\\r\\n\\r\\nfoldername\\r\\n-----011000010111000001101001--\\r\\n\\r\\n"
headers = {
 'Content-Type': "multipart/form-data; boundary=---011000010111000001101001",
 'X-API-TOKEN': "tokenID"
 }
conn.request("POST", "/API/v3/libraries/libraryID/graphics", payload, headers)
res = conn.getresponse()
data = res.read()
print(data.decode("utf-8"))

The error message with the python code is 

{"meta":{"httpStatus":"400 - Bad Request","error":{"errorMessage":"Missing Content-Type for file part. name=file","errorCode":"MFDP_3"},"requestId":"7a009aca-135f-49bc-b755-6ccfe8b5da1d"}}

but it seems I have specified content-type in the payload.