Python 3 with Requests trying to use Tumblr API, I get error 401?

I have Python 3 and I am trying to post to Tumblr via API link to API documentation. I keep getting an error 401 despite feeling like I am doing everything correctly. There is an official API client in Python 2 but that feels a bit hard to follow and all other mentions of it seem to be in PHP or Java. I also am not sure of the format to post in after the 401 error because the documentation doesn't give any explicit examples other than /post. My code:

import requests
from requests_oauthlib import OAuth1
#variables for later
client_key=""
client_secret=""
oauth_token=""
oauth_token_secret=""

#gets the values for the variables
with open("API.txt", 'r') as readAPI:
    readAPI.readline()
    client_key=readAPI.readline()[23:]
    client_secret=readAPI.readline()[23:]
    oauth_token=readAPI.readline()[23:]
    oauth_token_secret=readAPI.readline()[23:]
readAPI.close()

#prints them to double check they are being read correctly
print(client_key)
print(client_secret)
print(oauth_token)
print(oauth_token_secret)

#sets oauth for the connection
oauth = OAuth1(client_key,
               client_secret,
               oauth_token,
               oauth_token_secret)

#check post that should return various blog stats
r = requests.get("http://api.tumblr.com/v2/user/info" ,auth=oauth)

print(r)

I am 100% sure I am getting the client key, the client secret, oauth token and oauth token secret correct. I have double checked, the oauth tokens are both put in the file that is being read manually and they are printed before the connection attempt. I am 100% sure it is correct. I'm wondering if Tumblr's API is broken?

Edit: This is with print(repr())

'client_key'
'client_secret'
'oauth_token'
'oauth_token_secret'
{"meta":{"status":401,"msg":"Not Authorized"},"response":[]}

This is what happens after trying a new code and with Steven's method with JSON.

b'{"meta":{"status":401,"msg":"Not Authorized"},"response":[]}'

Solution

Instead of doing this:

print(client_key)

What is the output of this?

print(repr(client_key))

You're using readline, which includes a newline character at the end of each line:

$ cat foo.txt
key
secret
blabla

$ python3.4
>>> f = open("foo.txt")
>>> print(repr(f.readline()))
'key\n'
>>> print(repr(f.readline()))
'secret\n'
>>> print(repr(f.readline()))
'blabla\n'

Have you tried stripping the newline character off of each line?

Edit: Updating my post based on @user2853325's comments. Your code works for me under Python 3.4, requests==2.5.2, and requests-oauthlib==0.4.2.

API.json (redacted the keys/secrets):

{
    "client_key": "XXXXXXXXXXXXXXXXXXXXdG7zXIMcDidwQ5pMHuQTbxyhNINrCE",
    "client_secret": "XXXXXXXXXXXXXXXXXXXX72A5HQO1axydP5nlOWCTQx4ECfXfyX",
    "oauth_token": "XXXXXXXXXXXXXXXXXXXX8WAnqMBWaAdnGhnc4gWhJ4j6cufK1W",
    "oauth_token_secret": "XXXXXXXXXXXXXXXXXXXX8Kf82k65JzIcMU7QUp54ssPEzJd7my"
}

tumblr.py:

import json

import requests
from requests_oauthlib import OAuth1

#gets the values for the variables
with open("API.json") as f:
    credentials = json.load(f)

#prints them to double check they are being read correctly
print(credentials)

#sets oauth for the connection
oauth = OAuth1(
    credentials['client_key'],
    credentials['client_secret'],
    credentials['oauth_token'],
    credentials['oauth_token_secret']
)

#check post that should return various blog stats
r = requests.get("http://api.tumblr.com/v2/user/info", auth=oauth)
print(r)
print(r.content)

Output (redacted the oauth stuff):

$ bin/python tumblr.py
{'oauth_token_secret': 'XXXXXXXXXXXXXXXXXXXX8Kf82k65JzIcMU7QUp54ssPEzJd7my', 'client_secret': 'XXXXXXXXXXXXXXXXXXXX72A5HQO1axydP5nlOWCTQx4ECfXfyX', 'client_key': 'XXXXXXXXXXXXXXXXXXXXdG7zXIMcDidwQ5pMHuQTbxyhNINrCE', 'oauth_token': 'XXXXXXXXXXXXXXXXXXXX8WAnqMBWaAdnGhnc4gWhJ4j6cufK1W'}
<Response [200]>
b'{"meta":{"status":200,"msg":"OK"},"response":{"user":{"name":"lost-theory","likes":0,"following":2,"default_post_format":"html","blogs":[{"title":"Untitled","name":"lost-theory","posts":0,"url":"http:\\/\\/lost-theory.tumblr.com\\/","updated":0,"description":"","is_nsfw":false,"ask":false,"ask_page_title":"Ask me anything","ask_anon":false,"followed":false,"can_send_fan_mail":true,"share_likes":true,"likes":0,"twitter_enabled":false,"twitter_send":false,"facebook_opengraph_enabled":"N","tweet":"N","facebook":"N","followers":0,"primary":true,"admin":true,"messages":0,"queue":0,"drafts":0,"type":"public"}]}}}'

So now that I've tested your code out for myself:

How did you get the oauth_token and oauth_token_secret? I got mine by clicking "Explore API" on the Applications developer page.
You don't need to call readAPI.close(), as the with block automatically closes the file for you (see the official docs).
I used JSON for storing and reading the credentials, that way I'm 100% sure that I'm getting the correct strings. The code is cleaner too. I'm still suspicious about the way you're reading lines from the file and slicing them.
Try printing r.content in your code the same way I am. Does it give you a more descriptive error message than "401 Unauthorized"?