Quick Answer
The answer is to use the `if __name__ == '__main__':` guard, which ensures that a specific function like `run()` executes only when the script is run directly, not when it is imported as a module. This works because Python sets the special variable `__name__` to the string `'__main__'` for the file being executed as the main program, while setting it to the module’s name (e.g., `'my_module'`) when imported, causing the condition to fail. On the Certified Associate Python Programmer PCAP exam, this question tests your understanding of module execution control and script behavior, often appearing as a multiple-choice trap where a function runs unintentionally during import. A common mistake is forgetting that code outside this guard executes on import, so always wrap test or run logic inside this conditional. Memory tip: think of `__name__` as a name tag—when your script is the star of the show, it wears the `'__main__'` badge; when it’s just a guest in another script, it wears its own module name.
This PCAP practice question tests your understanding of modules and packages. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A Python script imports the module 'my_module'. The developer wants to ensure that when the script is run directly, it executes a specific function, but when imported as a module, that function is not executed. Which code snippet achieves this?
if __name__ == '__main__': run()
Why wrong: Double underscores are missing; correct is '__main__'.
if __name__ == '__main__': run()
This is the standard Python idiom for executable scripts.
if os.environ.get('RUN_MAIN'): run()
Why wrong: Environment variables are not the standard mechanism.
if sys.argv[0] == 'my_module': run()
Why wrong: sys.argv[0] is the script name, not reliable for imported modules.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
if __name__ == '__main__': run()
Option B is correct because the `if __name__ == '__main__':` guard is the standard Python idiom to check whether a script is being run directly (as the main program) or being imported as a module. When the script is executed directly, Python sets the special variable `__name__` to the string `'__main__'`, so the function `run()` is called. When the script is imported, `__name__` is set to the module's name (e.g., `'my_module'`), so the condition fails and `run()` is not executed.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
if __name__ == '__main__': run()
Why it's wrong here
Double underscores are missing; correct is '__main__'.
if __name__ == '__main__': run()
Why this is correct
This is the standard Python idiom for executable scripts.
Related concept
Read the scenario before looking for a memorised answer.
if os.environ.get('RUN_MAIN'): run()
Why it's wrong here
Environment variables are not the standard mechanism.
if sys.argv[0] == 'my_module': run()
Why it's wrong here
sys.argv[0] is the script name, not reliable for imported modules.
Common exam traps
Python Institute often tests the distinction between `__name__` and `sys.argv` or environment variables, trapping candidates who confuse the script's filename with the module's name or who think an external flag is needed to control execution.
Detailed technical explanation
Under the hood, when Python loads a script, it compiles the file and sets the global `__name__` variable based on how the file was loaded: `'__main__'` for the entry point script, or the module's fully qualified name for imports. This mechanism is part of Python's module system and is defined in PEP 299 and the Python execution model. A subtle behavior is that even if a script is run with `python -m my_module`, `__name__` is set to `'__main__'` for the top-level module, so the guard still works correctly for package entry points.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Modules and Packages — This question tests Modules and Packages — Read the scenario before looking for a memorised answer..
The correct answer is: if __name__ == '__main__': run() — Option B is correct because the `if __name__ == '__main__':` guard is the standard Python idiom to check whether a script is being run directly (as the main program) or being imported as a module. When the script is executed directly, Python sets the special variable `__name__` to the string `'__main__'`, so the function `run()` is called. When the script is imported, `__name__` is set to the module's name (e.g., `'my_module'`), so the condition fails and `run()` is not executed.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
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