IDis31's questions

It is common to find code with this form:

def hacer_algo():
    print("algo")

if __name__ == "__main__":
    hacer_algo()

Instead of, for example:

def hacer_algo():
    print("algo")

hacer_algo()

We also notice that the variable __name__is not initialized by us, but exists in the environment.

• What is the difference?
• Why prefer one over the other?
• What is it and how it works?

I have found blocks of code like this:

with a as b:
    c = b.algo()

It would look like some dynamic similar to namespaces, but the following code

a = 1
with a as b:
    print a, b

returns the following error:

AttributeError: __exit__

So what is the keyword for with, and how does it work? What is the role of __exit__?

I understand the differences between passing by value and passing by reference , but doing some research about Python found that it doesn't use the aforementioned models, but rather one called "pass by object". It appears to be similar to the model used in LISP.

What does pass by object mean? What are the differences between passing by object, by value, and by reference?

I would like to print numeric values ​​with decimals in their fraction form:

0.5 to 1/2
0.75 to 3/4
4.5 to 9/2

Is there a native library to perform the conversion? How is this conversion done?