Error in Pycharm

[Hudjefa]

I'm using Pycharm as a Python IDE. Is it advisable to do so?
I wrote a program and it gives me the following error messages (the code works, Pycharm says its a warning and a weak warning)

Error:
Name 'length' can be undefined
Name 'n' can be undefined
Multi-step list initialization can be replaced with a list literal

My code is (if required to help me):

numerator = float(input("Enter numerator: "))
denominator = float(input("Enter denominator: "))

numerator = int(round((numerator * 100 / denominator), 0))
denominator = 100

numbers_list = []
numbers_list.append(numerator)
numbers_list.append(numerator - 1)

sum_is_1 = False
difference_is_0 = False

test_number_1 = (numerator / 100) + ((numerator - 1) / 100)

doubling = 1

while not sum_is_1 and not difference_is_0:
    length = len(numbers_list)
    fractions_total = 0
    doubling = doubling * 2
    for i in range(length):
        numbers_list[i] = numbers_list[i] * 2
    for i in range(length - 1):
        numbers_list.insert(i + 1, numbers_list[i] - 1)
    length = len(numbers_list)
    for i in range(length):
        fractions_total = fractions_total + numbers_list[i] / (100 * doubling)
    test_number_2 = fractions_total
    if fractions_total >= 1:
        sum_is_1 = True
    difference = abs(test_number_1 - test_number_2)
    test_number_1 = test_number_2
    if difference <= 0.0001:
        difference_is_0 = True

print("For fraction " + str(numerator / denominator) +
      ", we can construct fractions <= " + str(numerator / denominator) +
      " such that their sum = 1")

print()

print("The list of numbers that had to be created")
print(numbers_list)

print()

print("the fractions are: ")
for i in range(length):
    print(numbers_list[i] / (100 * doubling))

print()

sum_1 = 0
for i in range(length):
    sum_1 = sum_1 + numbers_list[i] / (100 * doubling)
    sum_2 = sum_1 + numbers_list[i + 1] / (100 * doubling)
    if sum_2 >= 1:
        n = i + 1 # excluded
        break

sum_1 = 0
for i in range(n):
    sum_1 = sum_1 + (numbers_list[i] / (100 * doubling))
other_fraction = round(1 - sum_1, 5)

print("The fractions are: ")
for i in range(n):
    print(numbers_list[i] / (100 * doubling))
print(other_fraction)

What I intend to do is start off with a fraction. Say 3/10. We get to the next smaller fraction 2/10. Then I multiply both fractions by 2/2 = 1 and we get 6/20, 4/20. I can then get an in-between fraction 5/20. I repeat the process. I add these fractions up and check if the sum >= 1.