Calculating work during gas expansion is a common thermodynamics problem. Automating this with Python streamlines engineering analysis. When an ideal gas expands isothermally, the work done can be determined using the formula:

`W = nRT * ln(Vf/Vi)`

where **W** is the work done, **n** is the amount of gas in moles, **R** is the universal gas constant, **T** is the absolute temperature, **Vi** is the initial volume, **Vf** is the final volume, and **ln** is the natural logarithm. By creating a Python function to perform this calculation, you can quickly analyze different scenarios and support engineering decision-making.


import unittest
import user_code
import ast
import re   
import importlib
import csv
import unittest
import importlib
import math

class TestTask(unittest.TestCase):
    def test_work_standard_case(self):
        import user_code
        importlib.reload(user_code)
        func = getattr(user_code, 'isothermal_expansion_work', None)
        _dynamic_test(
            self,
            callable(func),
            "Function isothermal_expansion_work is defined",
            "Function isothermal_expansion_work is not defined"
        )
        if not callable(func):
            return
        result = func(1.0, 2.0, 1.0, 300)
        expected = 1.0 * 8.314 * 300 * math.log(2.0/1.0)
        _dynamic_test(
            self,
            abs(result - expected) < 1e-6,
            "Correct work for vi=1.0, vf=2.0, n=1.0, t=300",
            f"Expected {expected}, got {result}"
        )

    def test_work_different_values(self):
        import user_code
        importlib.reload(user_code)
        func = getattr(user_code, 'isothermal_expansion_work', None)
        _dynamic_test(
            self,
            callable(func),
            "Function isothermal_expansion_work is defined",
            "Function isothermal_expansion_work is not defined"
        )
        if not callable(func):
            return
        result = func(2.0, 4.0, 0.5, 350)
        expected = 0.5 * 8.314 * 350 * math.log(4.0/2.0)
        _dynamic_test(
            self,
            abs(result - expected) < 1e-6,
            "Correct work for vi=2.0, vf=4.0, n=0.5, t=350",
            f"Expected {expected}, got {result}"
        )

    def test_equal_volumes(self):
        import user_code
        importlib.reload(user_code)
        func = getattr(user_code, 'isothermal_expansion_work', None)
        _dynamic_test(
            self,
            callable(func),
            "Function isothermal_expansion_work is defined",
            "Function isothermal_expansion_work is not defined"
        )
        if not callable(func):
            return
        result = func(3.0, 3.0, 1.0, 300)
        _dynamic_test(
            self,
            abs(result) < 1e-10,
            "Returns zero when vi == vf",
            f"Expected 0 when vi == vf, got {result}"
        )

    def test_vf_less_than_vi(self):
        import user_code
        importlib.reload(user_code)
        func = getattr(user_code, 'isothermal_expansion_work', None)
        _dynamic_test(
            self,
            callable(func),
            "Function isothermal_expansion_work is defined",
            "Function isothermal_expansion_work is not defined"
        )
        if not callable(func):
            return
        result = func(2.0, 1.0, 1.0, 300)
        expected = 1.0 * 8.314 * 300 * math.log(1.0/2.0)
        _dynamic_test(
            self,
            abs(result - expected) < 1e-6 and result < 0,
            "Returns correct negative work value when vf < vi",
            f"Expected {expected} (negative), got {result}"
        )

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: Gas Expansion Work Calculation

Solution

Challenge: Gas Expansion Work Calculation

Solution