Structure of a Basic Python Program
Thomas J. Kennedy
1 Python Terminology
The term dunder refers to any item that is both preceded and followed by two underscores.
If you are familiar with operator overloading in C++…
bool operator==(const Book& lhs, const Book& rhs);
…or methods such as equals, toString, and hashCode in Java… the so-called Python dunder functions can be considered analogous (but not quite equivalent).
Our first example is the dunder main (i.e., __main__) block.
2 If __main__
The last chunk is what tells the Python interpreter what to run.
if __name__ == "__main__":
some_driver_function()
This allows us to run our script directly. If we import the Python script into a larger program… the __name__ == "__main__" will evaluate to False. This will allow us to call our functions from a larger program without having to rewrite any code.
The implications and importance of if __name__ == "__main__" cannot be fully discussed until we have, at the very least, discussed functions, modules, and imports later in the course.
3 A Little Better Than “Hello World”
Most programming introductions include a program that, as its name “Hello World” suggests prints…
Hello World
I abhor such examples. Let us do something slightly better.
"""
This is a short example module that contains a single driver function and
outputs a hardcoded name.
"""
def main():
name = "Tom"
print(f"Hello {name}!")
if __name__ == "__main__":
main()
This program outputs a hardcoded name (in this case Tom). I encourage you to type up the program and replace “Tom” with your name.
Note that print, f-strings, and variables will be covered in the next module.
4 Module docstring
The multi-line comment string at the top of the file is known as a module docstring.
"""
This is a short example module that contains a single driver function and
outputs a hardcoded name.
"""
It provides a brief overview of the modules as a whole. While our current program is quite simple… such documentation becomes quite useful when we start working with functions grouped into modules.
While some resources might call this block a comment… it is actually a multi-line string literal. Python does not have true multi-line comments.