Churn prediction is a key application of data science in startups, enabling you to identify which customers are likely to leave and take proactive measures to retain them. By using machine learning models like **logistic regression**, you can analyze patterns in customer data and estimate the likelihood of churn. Equally important is understanding which features—such as `usage frequency`, `account age`, or `support requests`—most strongly influence the model's predictions. This knowledge empowers you to target interventions and optimize your product or service for customer retention.


import unittest
import user_code
import ast
import re   
import importlib
import csv
import unittest
import importlib
import sys
import io
import numpy as np

class TestTask(unittest.TestCase):
    def test_logistic_regression_fitted(self):
        import user_code
        importlib.reload(user_code)
        model = getattr(user_code, 'model', None)
        _dynamic_test(
            self,
            hasattr(model, 'coef_'),
            "Logistic regression model is fitted and has coef_ attribute",
            "Model is not fitted or missing coef_ attribute."
        )

    def test_predictions_variable(self):
        import user_code
        importlib.reload(user_code)
        predictions = getattr(user_code, 'predictions', None)
        _dynamic_test(
            self,
            predictions is not None and isinstance(predictions, (np.ndarray, list)) and len(predictions) == 3,
            "Predictions variable exists and has length 3",
            f"Predictions variable is missing or has incorrect length: {predictions}"
        )
        # Should only contain 0s and 1s
        if predictions is not None:
            for p in predictions:
                _dynamic_test(
                    self,
                    p in [0, 1],
                    "Predictions contain only 0 and 1",
                    f"Prediction contains invalid value: {p}"
                )

    def test_feature_importance_variable(self):
        import user_code
        importlib.reload(user_code)
        feature_importance = getattr(user_code, 'feature_importance', None)
        _dynamic_test(
            self,
            feature_importance is not None and hasattr(feature_importance, 'index') and hasattr(feature_importance, 'values'),
            "feature_importance variable exists and is a pandas Series",
            f"feature_importance variable is missing or not a pandas Series: {feature_importance}"
        )
        # Check that all values are non-negative and sorted descending
        if feature_importance is not None:
            values = list(feature_importance.values)
            _dynamic_test(
                self,
                all(v >= 0 for v in values),
                "All feature_importance values are non-negative",
                f"feature_importance contains negative values: {values}"
            )
            _dynamic_test(
                self,
                all(values[i] >= values[i+1] for i in range(len(values)-1)),
                "feature_importance is sorted in descending order",
                f"feature_importance is not sorted descending: {values}"
            )

    def test_code_runs_without_errors(self):
        # This test ensures the code runs and prints expected output variables
        import user_code
        import importlib
        import sys
        import io
        f = io.StringIO()
        sys_stdout = sys.stdout
        sys.stdout = f
        try:
            importlib.reload(user_code)
        finally:
            sys.stdout = sys_stdout
        output = f.getvalue()
        _dynamic_test(
            self,
            "churn predictions for new customers:" in output.lower(),
            "Output includes churn predictions for new customers",
            f"Expected churn prediction output not found: {output}"
        )
        _dynamic_test(
            self,
            "feature importance for churn prediction:" in output.lower(),
            "Output includes feature importance for churn prediction",
            f"Expected feature importance output not found: {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: Churn Prediction Tool

Solution

Challenge: Churn Prediction Tool

Solution