Why use def main()?

python coding-style
Wizzard picture Wizzard · Oct 28, 2010 · Viewed 709.7k times · Source

I've seen some code samples and tutorials that use

def main():
    # my code here

if __name__ == "__main__":
    main()

But why? Is there any reason not do define your functions at the top of the file, then just write code under it? ie

def my_function()
    # my code here

def my_function_two()
    # my code here

# some code
# call function
# print(something)

I just wonder if there is any rhyme to the main?

Answer

Ignacio Vazquez-Abrams picture Ignacio Vazquez-Abrams · Oct 28, 2010

Without the main sentinel, the code would be executed even if the script were imported as a module.

Related questions

Styling multi-line conditions in 'if' statements?

Sometimes I break long conditions in ifs onto several lines. The most obvious way to do this is: if (cond1 == 'val1' and cond2 == 'val2' and cond3 == 'val3' and cond4 == 'val4'): do_something Isn't very very appealing …

Read More
How do I return multiple values from a function?

The canonical way to return multiple values in languages that support it is often tupling. Option: Using a tuple Consider this trivial example: def f(x): y0 = x + 1 y1 = x * 3 y2 = y0 ** y3 return (y0, y1, y2) However, this quickly …

Read More
Python `if x is not None` or `if not x is None`?

I've always thought of the if not x is None version to be more clear, but Google's style guide and PEP-8 both use if x is not None. Is there any minor performance difference (I'm assuming not), and is there …

Read More