def f1(x):
    if x > 1 or -1 < x < 1:
        return (x**2-x)/(x**2-1)
    elif x == 1:
        return 1/2
    else:
        return (x-x**2)/(x**2-1)

def f2(list1):
    seen=[]
    result = []
    for element in list1:
        if element not in seen:
            seen.append(element)
        else:
            if element not in result:
                result.append(element)
    return result

def f3(astring):
    result = []
    for letter in astring:
        if letter not in 'aei':
            result.append(letter)
    return "".join(result)

def f4():
    return [i**2 for i in range(1001) if i**2%10==5]

def f5(filename):
    ''' opens a file given by the filename to which the extension
        csv is added, and then calculates the sum of the values per
        line to be put into a file with the same filename, but extension
        txt
    '''
    with open(filename+'.csv') as infile, open(filename+'.txt', 'w') as outfile:
        for line in infile:
            suma = 0
            numbers=line.strip().split(',')
            for number in numbers:
                try:
                    suma += int(number)
                except:
                    pass
            print(suma, file = outfile)
    return

def f6(filename):
    with open(filename) as infile:
        count = 0
        for line in infile:
            for letter in line:
                if letter == 'a':
                    count += 1
        return count

def f7(x):
    try:
        float(x)
        return True
    except ValueError:
        return False

import random
def f8():
    secret = random.randint(0,100)
    while True:
        x = int(input('guess the number: '))
        if x < secret:
            print('your number is too small')
        elif x > secret:
            print('your number is too large')
        else:
            print('you got it')
            return