You are assigned to write a Python script that needs to execute a block of code only if a file exists at a specified location. How would you implement this control structure to check the existence of the file and execute the block of code?

To check the existence of a file in Python and execute a block of code if the file exists, you should use if os.path.exists(filename): .... This code snippet uses the os.path.exists function to check if the file exists before proceeding with the specified block of code.