Constructions like index = index + 1 are often found in Python, so the creators of the language added an abbreviated version: index += 1.

The only difference is how they're written. The interpreter will turn an abbreviated construction into its expanded form.

These abbreviations are called syntactic sugar because they make the process of writing code a little easier and more pleasant.

This form is especially common in loops, where we often change a counter and accumulate a result:

sum = 0
index = 1

while index <= 5:
    sum += index      # Same as sum = sum + index
    index += 1        # Same as index = index + 1

print(sum)  # => 15

Without abbreviated assignment, the loop body would be longer:

while index <= 5:
    sum = sum + index
    index = index + 1

There are abbreviated forms for all arithmetic operations and for string concatenation:

• a = a + 1 → a += 1
• a = a - 1 → a -= 1
• a = a * 2 → a *= 2
• a = a / 1 → a /= 1

Implement the function build_progress_bar(), which takes the number of completed steps and the total number of steps, then returns a progress indicator string.

Completed steps are shown with #, and remaining steps are shown with -. Try not to use built-in string methods in your solution.

build_progress_bar(0, 5)  # '-----'
build_progress_bar(3, 5)  # '###--'
build_progress_bar(5, 5)  # '#####'