Single player Hangman in Python
Your code is good but it may be overly complex. The more concise the code the easier it is to read (for me anyway). In this example below I have just used some example words, this code of course is just a quick example for demonstration. There is not anything in place if you get the word or want to guess the word etc. I couldn't really find a reason to use a class for simpler games because although the functions are 'closely related' in your functions, comprehension can save a lot of time and code. 

The while loop is useful because it gives a consistent input option which can be as user friendly as you make it. I think its essential for the users experience when making something like a text RPG. 

import random

words = ['cheese', 'biscuits', 'hammer', 'evidence'] 
word_choice = [i.lower() for i in random.choice(words)]
lives = 3
cor_guess = []
while True:
  print('Letters found: {}\nWord length: {}'.format(cor_guess, len(word_choice)))
  if lives == 0:
      print('Your dead homie!\nThe word was: ', word_choice)
      break
  guess = str(input('Guess a letter: '))
  if guess in word_choice:
      print(guess, 'is in the word!\n')
      cor_guess.append(guess)
  else:
      print('Your dying slowly!\n')
      lives -= 1


Example of the output:

Letters found: []
Word length: 8
Guess a letter: v
v is in the word!

Letters found: ['v']
Word length: 8
Guess a letter: i
i is in the word!

Letters found: ['v', 'i']
Word length: 8
Guess a letter: r
Your dying slowly!

Letters found: ['v', 'i']
Word length: 8
Guess a letter: b
Your dying slowly!

Letters found: ['v', 'i']
Word length: 8
Guess a letter: o
Your dying slowly!

Letters found: ['v', 'i']
Word length: 8
Your dead homie!
The word was:  ['e', 'v', 'i', 'd', 'e', 'n', 'c', 'e']