Visualizing truss structures and applied forces is crucial for understanding load paths. This challenge will help you automate truss visualization. In structural engineering, a **truss** is a framework composed of straight members connected at nodes. Being able to plot these elements and show how **forces** act on the structure makes analysis and communication much clearer. Using `python` and `matplotlib`, you can quickly generate accurate diagrams from data, making your workflow more efficient and your results more understandable.


import unittest
import user_code
import ast
import re   
import importlib
import csv
import unittest
import importlib
import matplotlib
matplotlib.use('Agg')
import matplotlib.pyplot as plt
import sys

class TestTask(unittest.TestCase):
    def setUp(self):
        global user_code
        import user_code
        importlib.reload(user_code)
        self.user_code = user_code
        # Sample data for tests
        self.nodes = [(0, 0), (2, 0), (1, 1.5)]
        self.members = [(0, 1), (1, 2), (2, 0)]
        self.forces = [(1, 0, -1), (2, 1, 0)]

    def test_plot_truss_members(self):
        # Patch plt.subplots to capture lines
        lines_drawn = []
        orig_plot = plt.Axes.plot
        def fake_plot(axself, x, y, *args, **kwargs):
            lines_drawn.append((tuple(x), tuple(y)))
            return orig_plot(axself, x, y, *args, **kwargs)
        plt.Axes.plot = fake_plot
        try:
            self.user_code.plot_truss(self.nodes, self.members, [])
        finally:
            plt.Axes.plot = orig_plot
        # Check that each member line is drawn between correct nodes
        expected_lines = set()
        for n1, n2 in self.members:
            x_vals = (self.nodes[n1][0], self.nodes[n2][0])
            y_vals = (self.nodes[n1][1], self.nodes[n2][1])
            expected_lines.add((x_vals, y_vals))
        actual_lines = set(lines_drawn)
        _dynamic_test(
            self,
            expected_lines.issubset(actual_lines),
            "Function draws all truss members as lines between the specified nodes.",
            f"Expected lines: {expected_lines}, but got: {actual_lines}"
        )

    def test_plot_truss_nodes_and_labels(self):
        # Patch plt.Axes.plot and plt.Axes.text to capture node points and labels
        node_points = []
        node_labels = []
        orig_plot = plt.Axes.plot
        orig_text = plt.Axes.text
        def fake_plot(axself, x, y, *args, **kwargs):
            if args and args[0] == 'ko':
                node_points.append((x[0], y[0]))
            return orig_plot(axself, x, y, *args, **kwargs)
        def fake_text(axself, x, y, s, *args, **kwargs):
            node_labels.append((x, y, s))
            return orig_text(axself, x, y, s, *args, **kwargs)
        plt.Axes.plot = fake_plot
        plt.Axes.text = fake_text
        try:
            self.user_code.plot_truss(self.nodes, self.members, [])
        finally:
            plt.Axes.plot = orig_plot
            plt.Axes.text = orig_text
        # Each node point should be drawn
        node_coords = set(self.nodes)
        actual_points = set(node_points)
        _dynamic_test(
            self,
            node_coords.issubset(actual_points),
            "Function marks each node as a point.",
            f"Expected node points: {node_coords}, got: {actual_points}"
        )
        # Each node label should be present
        expected_labels = {f'N{i}' for i in range(len(self.nodes))}
        actual_labels = {label for _, _, label in node_labels}
        _dynamic_test(
            self,
            expected_labels.issubset(actual_labels),
            "Function labels each node with the correct index.",
            f"Expected node labels: {expected_labels}, got: {actual_labels}"
        )

    def test_plot_truss_forces_and_labels(self):
        # Patch ax.arrow and ax.text to capture arrows and force labels
        arrows = []
        force_labels = []
        orig_subplots = plt.subplots
        orig_arrow = plt.Axes.arrow
        orig_text = plt.Axes.text
        def fake_arrow(axself, x, y, dx, dy, *args, **kwargs):
            arrows.append((x, y, dx, dy))
            return orig_arrow(axself, x, y, dx, dy, *args, **kwargs)
        def fake_text(axself, x, y, s, *args, **kwargs):
            force_labels.append((x, y, s))
            return orig_text(axself, x, y, s, *args, **kwargs)
        plt.Axes.arrow = fake_arrow
        plt.Axes.text = fake_text
        try:
            self.user_code.plot_truss(self.nodes, self.members, self.forces)
        finally:
            plt.Axes.arrow = orig_arrow
            plt.Axes.text = orig_text
        # Each force should be drawn as an arrow at the correct node with correct direction
        expected_arrows = set()
        for node_idx, fx, fy in self.forces:
            x, y = self.nodes[node_idx]
            expected_arrows.add((x, y, fx, fy))
        actual_arrows = set(arrows)
        _dynamic_test(
            self,
            expected_arrows.issubset(actual_arrows),
            "Function draws arrows for all applied forces at the correct node positions, with direction and magnitude matching the force components.",
            f"Expected arrows: {expected_arrows}, got: {actual_arrows}"
        )
        # Each force label should be present
        expected_force_labels = {f'F{node_idx}' for node_idx, _, _ in self.forces}
        actual_force_labels = {label for _, _, label in force_labels if label and label.startswith('F')}
        _dynamic_test(
            self,
            expected_force_labels.issubset(actual_force_labels),
            "Function labels each force arrow with the correct node index.",
            f"Expected force labels: {expected_force_labels}, got: {actual_force_labels}"
        )

def _dynamic_test(test_case, condition, success_message, failure_message):
    if condition:
        test_case._testMethodName = success_message
        test_case.assertTrue(True, success_message)
    else:
        test_case._testMethodName = failure_message
        test_case.fail(failure_message)

def normalize_text(text):
    text = text.lower()
    text = re.sub(r"\\s{2,}", " ", text)
    text = re.sub(r"\\s*([,:?])\\s*", r"\\1 ", text)
    return text.strip()

def change_var(code: str, var_name: str, value: str) -> str:
    tree = ast.parse(code)
    lines = code.splitlines()
    changed = False
    # Collect all assignment nodes to modify
    assign_nodes = [
        (i, node)
        for i, node in enumerate(tree.body)
        if isinstance(node, ast.Assign)
        and any(isinstance(target, ast.Name) and target.id == var_name for target in node.targets)
    ]

    # If nothing to change, return unmodified code
    if not assign_nodes:
        return code

    # Perform replacements for all matching assignments (from last to first to not break line offsets)
    for i, node in reversed(assign_nodes):
        start_line = node.lineno - 1
        line = lines[start_line]
        indent = ' ' * (len(line) - len(line.lstrip()))
        lines[start_line] = f"{indent}{var_name} = {value}"
        next_line = len(lines)
        for next_node in tree.body[i+1:]:
            if hasattr(next_node, 'lineno'):
                next_line = next_node.lineno - 1
                break
        if next_line > start_line + 1:
            lines[start_line+1:next_line] = []
        changed = True

    return '\\n'.join(lines) if changed else code

if __name__ == "__main__":
    unittest.main()


test_main.py

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Challenge: Visualize Truss Forces

Solution

Challenge: Visualize Truss Forces

Solution