Replace blanks with letter

[eschneider92 at comcast.net]

Thanks. I am running into a bunch of problems with the following code, all of which are clear when running the program

import random
letters='abcdefg' 
blanks='_'*len(letters) 
print('type letters from a to g')
print(blanks)
for i in range(len(letters)):
    if letters[i] in input(): 
        blanks = blanks[:i] + letters[i] + blanks[i+1:]
        print(blanks)

If anyone could post an example of how to correctly code this, I would appreciate it. I can't seem to figure it out.

I'll definitely heed Fabio's advice for future reference, but I don't think it's related to the problems I'm currently experiencing. If it is, and I'm just not getting it (most likely the case), please post an example of how to implement his code advice in doing what I wish to accomplish here.