Drawing went well except for the last row due to a possible logic error

Question

So I want to draw stacked rows of circles in symmetry. Please bear with me for a second because the code is pretty long.

# DRAWING THE DIAGRAM
pen = turtle.Turtle() # use turtle pen
pen.speed(-1) # speed of pen
pen.hideturtle() # hide the turtle
radius = 10 # radius of the symmetrical tubes
big_radius = 1.10*radius*max(columns) # radius of the shell of the heat exchanger wrt number of max columns
pen.circle(big_radius) # draw the shell
increment = 10
pen.pu()
#  CALCULATE MOST TUBES FIRST AKA MAX COLUMNS (ALSO TELLS US WHICH ROW IT IS)
for i in range(int(max(columns)/2)): # cross section is symmetrical hence columns/2 (drawing on the positive x-axis)
    pen.goto(increment, big_radius-radius)
    pen.pd()
    pen.circle(radius)
    pen.pu()
    pen.forward(radius*2)
    increment += 20

pen.pu()
radius *= -1 # this is to achieve symmetry on the negative axis
increment = -10
for i in range(int(max(columns)/2)): # as above, but now drawing on negative x-axis to maintain symmetry
    pen.goto(increment, big_radius - radius)
    pen.pd()
    pen.circle(radius)
    pen.pu()
    pen.forward(radius * 2)
    pen.pd()
    increment -= 20
pen.pu()

radius *= -1 # initialize to positive axis
increment = 10 # initialize to positive axis

middle_row = max(dict, key=dict.get)
# 1st row after the middle row (+ve y-axis, x-axis)
for i in range(1,2):
    pen.goto(increment,(big_radius + radius))
    for j in range(int(dict[middle_row-i]/2)):
        pen.pd()
        pen.circle(radius)
        pen.pu()
        pen.forward(radius * 2)
        increment +=20

**# subsequent rows after the first row (+ve x-axis) [MAIN CULPRIT]
for i in range(2,middle_row):
    increment = 10
    pen.goto(increment,big_radius + i*(radius+5))
    for j in range(int(dict[middle_row-i]/2)):
        pen.pd()
        pen.circle(radius)
        pen.pu()
        pen.forward(radius * 2)
        increment += 20**

# for 1st row after middle row (-ve x-axis)
for i in range(1,2):
    increment = -10
    pen.goto(increment,(big_radius + radius))
    for j in range(int(dict[middle_row-i]/2)):
        pen.pd()
        pen.circle(radius)
        pen.pu()
        pen.backward(radius * 2)
        increment -= 20

**# subsequent rows after the first row (-ve x-axis) [MAIN CULPRIT]
for i in range(2,middle_row):
    increment = -10
    pen.goto(increment,big_radius + i*(radius+5))
    for j in range(int(dict[middle_row-i]/2)):
        pen.pd()
        pen.circle(radius)
        pen.pu()
        pen.backward(radius * 2)
        increment -= 20**

radius *= -1 # initialize to negative y-axis

# 1st row after the middle row (-ve y-axis, -ve x-axis)
for i in range(1,2):
    increment = -10
    pen.goto(increment,(big_radius + radius))
    for j in range(int(dict[middle_row-i]/2)):
        pen.pd()
        pen.circle(radius)
        pen.pu()
        pen.forward(radius * 2)
        increment += 20

# subsequent rows after the first row (-ve x-axis)
for i in range(2,middle_row):
    increment = -10
    pen.goto(increment,big_radius + i*(radius-5))
    for j in range(int(dict[middle_row-i]/2)):
        pen.pd()
        pen.circle(radius)
        pen.pu()
        pen.forward(radius * 2)
        increment -= 20

# 1st row after the middle row (+ve x-axis)
for i in range(1,2):
    increment = 10
    pen.goto(increment,(big_radius + radius))
    for j in range(int(dict[middle_row-i]/2)):
        pen.pd()
        pen.circle(radius)
        pen.pu()
        pen.backward(radius * 2)
        increment += 20

**# subsequent rows after the first row (+ve x-axis) [MAIN CULPRIT]
for i in range(2,middle_row):
    increment = 10
    pen.goto(increment,big_radius + i*(radius-5))
    for j in range(int(dict[middle_row-i]/2)):
        pen.pd()
        pen.circle(radius)
        pen.pu()
        pen.backward(radius * 2)
        increment += 20**

I highlighted the code that probably contributed to this effect with [MAIN CULPRIT]. Everything worked except for the final top and bottom rows and I can't seem to figure out the issue other than a logic error in my code.

Image of said figure

Answer 1

It seems to me this code would be easier to debug if we reduced your 18 for loops to just 2:

from turtle import Screen, Pen

dictionary = {2: 2, 3: 4, 4: 6, 5: 8}  # mapping of row # -> row width
columns = dictionary.values()

RADIUS = 10 # RADIUS of the symmetrical tubes
BIG_RADIUS = 1.10 * RADIUS * max(columns)

screen = Screen()

pen = Pen()
pen.hideturtle()
pen.speed('fastest')

pen.penup()
pen.sety(-BIG_RADIUS)
pen.pendown()
pen.circle(BIG_RADIUS)
pen.penup()

max_rows = max(dictionary)
pen.sety(max_rows * RADIUS)

for row in range(2, 2 * max_rows - 1):
    columns = dictionary[row if row < max_rows else 2 * max_rows - row]

    pen.setx(-RADIUS * (columns - 1))

    for _ in range(columns):
        pen.pendown()
        pen.circle(RADIUS)
        pen.penup()
        pen.setx(pen.xcor() + RADIUS*2)

    pen.sety(pen.ycor() - RADIUS*2)

screen.exitonclick()

You didn't supply dict so I had to guess -- adjust as needed. I changed the code to keep the image centered on the window to simplify the math. A couple of programming notes:

 pen.speed(-1)

That's not a valid argument value for speed(). Also, don't (re)use the names of built-in types for your variables:

 dict[middle_row-i]

Use something else other than dict in this case.