urllib & python3: HTTP Error 405: Method Not Allowed - json

Question

I am trying to do a simple authentication using Python3 and urllib on an API that should return account balances.
The code I have is the following:
import urllib
import urllib.request
import json
id = "nkkhuz6" # fake
secret = "s9MeR0J9yxtndLBPVA" # fake
auth_str = id + ":" + secret
def getBalances():
values = {'u' : auth_str}
data = urllib.parse.urlencode(values)
data = data.encode('utf-8') # data should be bytes
request = urllib.request.Request(url = "https://api.com", data = data)
with urllib.request.urlopen(request) as f:
print(json.loads(f.read().decode('utf-8')))
However when I run getBalances() I get the following errors:
Adriaans-MacBook-Pro:Documents adriaanjoubert$ python3 main.py
Traceback (most recent call last):
File "main.py", line 96, in <module>
getBalances()
File "main.py", line 19, in getBalances
with urllib.request.urlopen(request) as f:
File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/urllib/request.py", line 161, in urlopen
return opener.open(url, data, timeout)
File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/urllib/request.py", line 469, in open
response = meth(req, response)
File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/urllib/request.py", line 579, in http_response
'http', request, response, code, msg, hdrs)
File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/urllib/request.py", line 507, in error
return self._call_chain(*args)
File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/urllib/request.py", line 441, in _call_chain
result = func(*args)
File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/urllib/request.py", line 587, in http_error_default
raise HTTPError(req.full_url, code, msg, hdrs, fp)
urllib.error.HTTPError: HTTP Error 405: Method Not Allowed
I am sure the URL is correct and if I append a trailing / I get the error urllib.error.HTTPError: HTTP Error 404: Not Found
When I run the following code I do get my account balances:
cmd = """curl -u """ + auth_str + """ https://api.com/"""
os.system(cmd)
What am I doing wrong? I would like to use urllib so that I can store the stuff I get back from the API in a variable.