Issue with triangles borders in Matplotlib

I am facing an issue with drawing triangle borders using Matplotlib in Python. I want to create a specific pattern, but I'm encountering unexpected behavior. I need assistance in identifying and resolving the problem.

this is my code

import numpy as np
import matplotlib.pyplot as plt
N = 5
A = np.array([(x, y) for y in range(N, -1, -1) for x in range(N + 1)])
t = np.array([[1, 1], [-1, 1]])
A = np.dot(A, t)

# I have defined a triangle
fig = plt.figure(figsize=(10, 10))
triangle = fig.add_subplot(111)

X = A[:, 0].reshape(N + 1, N + 1)
Y = A[:, 1].reshape(N + 1, N + 1)

for i in range(1, N + 1):
    for j in range(i):
        line_x = np.array([X[i, j + 1], X[i, j], X[i - 1, j]])
        line_y = np.array([Y[i, j + 1], Y[i, j], Y[i - 1, j]])
        triangle.plot(line_y,line_x,  color='black', linewidth=1)

plt.show()

but I am getting this image, as u can see,

At corner extra lines are coming, as i encircled it. I dont want this extra line, i tried to solved it using loop, eventhough one extra line will keep remain

for i in range(6):
    if i == N-1 :
        for j in range(i-1):
            line_x = np.array([X[i , j+1], X[i, j],X[i-1, j]])
            line_y = np.array([Y[i, j+1], Y[i, j], Y[i-1, j]])
            triangle.plot(line_y, line_x, color='black', linewidth=1)
        pass
    else:
        for j in range(i):
            line_x = np.array([X[i , j+1], X[i, j],X[i-1, j]])
            line_y = np.array([Y[i, j+1], Y[i, j], Y[i-1, j]])
            triangle.plot(line_y,line_x, color='black', linewidth=1)
        pass  

plt.show() kindly resolve the issue

The lines you want to delete belong to the triangules generated in the first (i = 1, j = 0) and last (i = N, J = N - 1) iterations of the nested for loops:

import numpy as np
import matplotlib.pyplot as plt

N = 5
A = np.array([(x, y) for y in range(N, -1, -1) for x in range(N + 1)])
t = np.array([[1, 1], [-1, 1]])
A = np.dot(A, t)

# I have defined a triangle
fig = plt.figure(figsize=(10, 10))
triangle = fig.add_subplot(111)

X = A[:, 1].reshape(N + 1, N + 1)
Y = A[:, 0].reshape(N + 1, N + 1)

for i in range(1, N + 1):
    for j in range(i):
        if i == 1: # Lower right triangle
            line_x = np.array([X[i, j + 1], X[i, j]])
            line_y = np.array([Y[i, j + 1], Y[i, j]])
        elif j == N - 1: # Upper right triangle
            line_x = np.array([X[i, j], X[i - 1, j]])
            line_y = np.array([Y[i, j], Y[i - 1, j]])
        else:
            line_x = np.array([X[i, j + 1], X[i, j], X[i - 1, j]])
            line_y = np.array([Y[i, j + 1], Y[i, j], Y[i - 1, j]])
        triangle.plot(line_x, line_y,  color='black', linewidth=1)

plt.show()