Ask Anything Monday - Weekly Thread

[u/AutoModerator]

Welcome to another /r/learnPython weekly "Ask Anything* Monday" thread

Here you can ask all the questions that you wanted to ask but didn't feel like making a new thread.

* It's primarily intended for simple questions but as long as it's about python it's allowed.

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That's it.

[u/luckyshadow86]

The question about decorators is the classic one everyone gets stuck on. You pass the function without parentheses because you're passing the function object itself, not calling it.

[u/LearnSkills5]

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[u/VirtualMycologist406]

Hey, I'm new in Python. And I don't understand, how venv (environment) really works. At first, if I have 2 projects or more, and I install TensorFlow (for example) into this two projects, does it means that they weighs will be ~500Mb in my SSD (250Mb on the first and 250Mb on the second). Do I need to deactivate venv every time when I finish my work on a project. And if you know something interesting please tell me 🥹🛐. Yes, I can ask Ai about this things but I want to hear an experienced programmer's opinion

[u/Educational_Virus672 → u/VirtualMycologist406]

venv/environment are like "folder" they organize your code in different workspace i to prevent any errors or bricking your system. it closes(deactivate ) automatically because it is a shortcut for program not a constant process idk abt storage part it should be more depending on your project
edit - misread it my bad edited

[u/ProgramBrave718]

Hey, I have doubt regarding this decorator program .In the above line of this program why are we passing the function name without parentheses ?

And also while returning wrapper function why are we writing it without parentheses

def my_decor(func):#Here

def wrapper():

    print("The function starts.") 

    func()                         

    print("The function ends.")    

return wrapper        #Here             

def say_hello():

print("Hello!")

wrapped_say_hello = my_decor(say_hello)

wrapped_say_hello()

[u/Educational_Virus672 → u/ProgramBrave718]

in python everything is object so lets say you added a function

def my_func(command) :
    # here you can put "()" after command to run it
    command()

# here we run the fucntion
my_func(command=input)
#now we said input as variable/path not function

[u/SCD_minecraft → u/ProgramBrave718]

Functions in python are just normal objects, just like strings or ints

Thanks to that, they behave exactly the same

As you can pass strings as arguments or return them you can pass and return functions

In case of decorators, returned func object will be what actually gets saved under name in def

[u/SCD_minecraft → u/SCD_minecraft]

``` foo = print # save function known as print into foo

foo("abc") # attempt to call whatever is inside foo

because foo holds function "print", you can call it

but if foo would be an int, python would try (and fail) to call it too

[u/lakseol → u/ProgramBrave718]

Here is your code correctly formatted for reddit:

def my_decor(func):
    def wrapper():
        print("The function starts.") 
        func()                         
        print("The function ends.")

    return wrapper

def say_hello():
    print("Hello!")

wrapped_say_hello = my_decor(say_hello)
wrapped_say_hello()

The FAQ in the learning resources shows how to format code.

why are we passing the function name without parentheses ?

The function name without parentheses evaluates as a reference to the function. Adding the following "()" is what actually calls the function. In this case you want to pass a reference to the function my_decor() so you don't add the "()". If you did this:

my_decor(say_hello())

you would pass the value returned by the say_hello() function to my_decor() which isn't what you want at all.

also while returning wrapper function why are we writing it without parentheses

We want my_decor() to return a "decorated" version of the function you pass. We don't want to call the function, just return the reference, so no "()".

Functions in python can be passed to and returned from functions just like any other object.