What will happen if you call a function that has not been defined?

• A. An error will occur and the program will terminate
• B. The function will return None
• C. The program will continue to run normally
• D. The function will execute with default values

Answer: (A)

When you call a function that has not been defined in Python, an error will occur, specifically a NameError. This error indicates that the name of the function is not recognized because it has not been defined anywhere in the current scope. As a result, the program cannot proceed with executing the script as it cannot locate the function definition to carry out the necessary operations.

This behavior is critical for maintaining code reliability; if the interpreter encounters an undefined function, it must alert the programmer immediately rather than guessing what the code is supposed to do. Other options do not apply in this scenario because the program's flow cannot continue in the absence of a valid function call, nor can it return a value (like None) or execute with defaults since the function itself does not exist.