In AC circuit analysis, **phasor representation** allows you to solve for voltages and currents using complex numbers. For a **series RLC circuit**, the total impedance `Z` is given by the formula:

`Z = R + j(ωL - 1/(ωC))`

where `R` is resistance, `L` is inductance, `C` is capacitance, `ω` (omega) is the angular frequency (`ω = 2πf`), and `j` is the imaginary unit. The **current amplitude** `I` in the circuit is found using Ohm's Law for AC: `I = V / |Z|`, where `V` is the voltage amplitude and `|Z|` is the magnitude of the impedance. The **phase angle** `θ` between the source voltage and the current is given by the argument (angle) of the impedance: `θ = arctan((ωL - 1/(ωC))/R)`.


import unittest
import user_code
import ast
import re   
import importlib
import csv
import unittest
import importlib
import io
import math
import cmath
from contextlib import redirect_stdout

class TestTask(unittest.TestCase):
    def test_impedance_calculation(self):
        import user_code
        importlib.reload(user_code)
        f = io.StringIO()
        with redirect_stdout(f):
            user_code.solve_series_rlc(100, 0.1, 10e-6, 50, 10)
        output = f.getvalue()
        # Calculate expected impedance
        R = 100
        L = 0.1
        C = 10e-6
        f_ = 50
        omega = 2 * math.pi * f_
        X_L = omega * L
        X_C = 1 / (omega * C)
        Z = complex(R, X_L - X_C)
        expected = f"Impedance: {Z}"
        _dynamic_test(
            self,
            normalize_text(expected) in normalize_text(output),
            f"Correct impedance calculated and printed: {Z}",
            f"Expected impedance output '{expected}', got '{output}'",
        )

    def test_current_amplitude(self):
        import user_code
        importlib.reload(user_code)
        f = io.StringIO()
        with redirect_stdout(f):
            user_code.solve_series_rlc(100, 0.1, 10e-6, 50, 10)
        output = f.getvalue()
        # Calculate expected current amplitude
        R = 100
        L = 0.1
        C = 10e-6
        f_ = 50
        V_ampl = 10
        omega = 2 * math.pi * f_
        X_L = omega * L
        X_C = 1 / (omega * C)
        Z = complex(R, X_L - X_C)
        Z_magnitude = abs(Z)
        current_amplitude = V_ampl / Z_magnitude
        expected = f"Current amplitude: {current_amplitude}"
        _dynamic_test(
            self,
            normalize_text(expected) in normalize_text(output),
            f"Correct current amplitude calculated and printed: {current_amplitude}",
            f"Expected current amplitude output '{expected}', got '{output}'",
        )

    def test_phase_angle(self):
        import user_code
        importlib.reload(user_code)
        f = io.StringIO()
        with redirect_stdout(f):
            user_code.solve_series_rlc(100, 0.1, 10e-6, 50, 10)
        output = f.getvalue()
        # Calculate expected phase angle
        R = 100
        L = 0.1
        C = 10e-6
        f_ = 50
        omega = 2 * math.pi * f_
        X_L = omega * L
        X_C = 1 / (omega * C)
        Z = complex(R, X_L - X_C)
        phase_angle_rad = cmath.phase(Z)
        phase_angle_deg = math.degrees(phase_angle_rad)
        expected = f"Phase angle (degrees): {phase_angle_deg}"
        _dynamic_test(
            self,
            normalize_text(expected) in normalize_text(output),
            f"Correct phase angle calculated and printed: {phase_angle_deg}",
            f"Expected phase angle output '{expected}', got '{output}'",
        )

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: Series RLC Circuit Solver

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