Q:

Text Duplicate filter in Python 3.7

I wrote this program just to remove duplicates from wordlist used for brute-force, but it can be used for every txt file i guess. 
It is a pretty long program for what it does, and I'm sure there is a way I can make it easier and better for everyone to look at. 
I'm still a beginner in python. 
def wordcount_initial():  # count the numbre of words in the input file
    global num_words_initial

    with open(file_initial, 'r') as f:
        for line in f:
            words = line.split()
            num_words_initial += len(words)

def dupfilter():
    content = open(file_initial, "r").readlines()
    content_set = set(content)  # filter duplicates
    cleandata = open(file_final, "w+")  # write the text filtered in the new   file

    for line in content_set:
        cleandata.write(line)

def wordcount_final():  # count number of words in the new file
    global num_words_final

    with open(file_final, 'r') as f:
        for line in f:
            words = line.split()
            num_words_final += len(words)

if __name__ == '__main__':
    num_words = 0
    num_words_initial = 0
    num_words_final = 0

    ready = False
    while not ready:
        file_initial = input("What is the name of the text?") 

        file_final = input("How do you want to name the filted file?") 

        if file_initial and file_final ! = "":

            wordcount_initial()
            ready = True

    dupfilter()

    wordcount_final()

    print("Number of duplicates filtered:" + str(num_words_initial - num_words_final))
    input("\nPress <ENTER> to quit the program.") 

A:

You should not use global variables unless you really need to.  Instead, pass relevant parameters as arguments to the functions and return the results.  This makes them actually reusable.  Currently you have two functions to count the initial and final number of words, when you could just have a word_count function:
def wordcount(file_name):
    """count the number of words in the file"""
    with open(file_name) as f:
        return sum(len(line.split()) for line in f) 

def dupfilter(file_initial, file_final):
    with open(file_initial) as in_file, open(file_final, "w") as out_file:
        out_file.writelines(set(in_file.readlines()))

if __name__ == '__main__':
    while True:
        file_initial = input("What is the name of the text?") 
        file_final = input("How do you want to name the filtered file?") 
        if file_initial and file_final and file_initial ! = file_final:
            break

    num_words_initial = wordcount(file_initial)
    dupfilter(file_initial, file_final)
    num_words_final = wordcount(file_final)

    print("Number of duplicates filtered:", num_words_initial - num_words_final)
    input("\nPress <ENTER> to quit the program.") 

I also used sum with a generator expression to simplify the wordcount function, used with to ensure that files are properly closed. 
In addition, I replaced the while not ready loop with a while True loop and an explicit break.  This is much more common in Python, especially for user input. 
Note that if file_initial and file_final ! = "" is only incidentally the same as if file_initial ! = "" and file_final ! = "" because non-empty strings are truthy.  This is why it is also equivalent to if file_initial and file_final.  But for example x and y == 3 is not the same as x == 3 and y == 3. 
You also don't need to call str on things to be printed, print does that for you if necessary. 

Note that using set does not guarantee the same order as the original file, for that you would want to use the itertools recipe unique_everseen:

from itertools import filterfalse

def unique_everseen(iterable, key=None):
    "List unique elements, preserving order.  Remember all elements ever seen." 
    # unique_everseen('AAAABBBCCDAABBB') --> A B C D
    # unique_everseen('ABBCcAD', str.lower) --> A B C D
    seen = set()
    seen_add = seen.add
    if key is None:
        for element in filterfalse(seen.__contains__, iterable):
            seen_add(element)
            yield element
    else:
        for element in iterable:
            k = key(element)
            if k not in seen:
                seen_add(k)
                yield element

def dupfilter(file_initial, file_final):
    with open(file_initial) as in_file, open(file_final, "w") as out_file:
        out_file.writelines(unique_everseen(in_file))

A:

Thanks for sharing your code! 
I'll begin by pointing out you don't need global variable, and you should avoid them when possible.  Very often it only does make your code less readable and more fragile. 
Here your function wordcount_initial could be rewritten as: (same idea for wordcount_final)
def wordcount_initial(input_file):
    """Return the number of words in the file given in parameter

       :param input_file: A file name
       :type input_file: string 
       :return: The number of words in the file `input_file`
       :rtype: int
    """
    num_words_initial = 0
    with open(input_file, 'r') as f:
        for line in f:
            words = line.split()
            num_words_initial += len(words)
    return num_words_initial

There are a few changes here:

Removed num_words_initial as a global and return it's value at the end of the function.  It's much more clean to return value that way when you can.  It also help when you want to test your functions. 
Gives input_file as a parameter of your function instead of relying on another global.  It makes your function more reusable. 
And I transformed your comment in docstring that can be used to generate documentation for your code.  See ReStrusctured and sphinx for more information.  Ideally every function should be documented (and every module too)

Another remark, you name your function dupfilter, but every other name in your code has the format first_last which is a bit inconsistant.  Also, don't try to gain a few letters when typing, write duplicatefilter or better (in my opinion) filter_duplicate. 
Naming is always a bit subjective, use your best judgement. 
And finally in your __main__ you could have put the logic for initialising the name of the file into another function but that's not very important. 
On a more positive note I like how you laid out your code, it is well spaced, most of the name are clear when you read them and you have comment which is often important. 
Nice job!