Unlike languages like Go, the main() function isn’t a special, built-in part of Python. Instead, it’s a convention that people use to execute code. It’s typically paired with an if __name__ == "__main__": block, that looks like this:
if __name__ == "__main__":
main()Although main() isn’t special in python, the __name__ variable is. If we run a script directly (e.g. by running python my_script.py or uv run my_script.py), then the python interpreter sets the __name__ variable for that script to __main__. Whereas if we import my_script.py from another script, the __name__ variable will be set to its module name (e.g. my_script in this case).
This is a useful pattern because it lets us define logic that will only be executed if a python script is run directly. For example, imagine the following script:
#my_script.py
def hello(name):
return f"Hello, {name}"
def main():
nm = "Eric"
x = hello(nm)
print(x)
if __name__ == "__main__":
main()If we ran python my_script.py directly, we’d get "Hello, Eric", like we would expect. But if we had another script that imported this script, we could access the hello() function without executing the main() function:
#another_script.py
from my_script import hello
print(hello("Kendall"))