What is parentheses in python

What do parentheses do when used after a variable in Python?

Right now, I’m having trouble understanding the function of empty parentheses at the end of method names, built-in or user-created. In Python, functions and methods are first-order objects.

What do parentheses do when used after a variable in Python?

This question might be stupid but I don’t know Python well enough to know what’s going on. So I was trying to learn TensorFlow and noticed this weird invocation:

model = Sequential( # . ) predictions = model(x_train[:1]).numpy() 

Can someone please explain what model(x_train[:1]) is doing here? From what I can tell, model is an object that’s already constructed above? Is this using the object as a method/function? Or is something else going on here?

In this case the Tensorflow authors have provided an implementation for the __call__ «magic method» in the tf.keras.Sequential class hierarchy.

This allows you to invoke the instance of the object as-if it were a function. The call to model = Sequential(. ) initialises the class itself via the __init__ constructor. The model() calls into the __call__ magic method.

Tensorflow and torch use this as convenience wrapper for a forward pass through the network (in most cases).

Python 3.x — Why do I have parenthesis when I print, Why do I have parenthesis when I print strings plus variables in Python34? Ask Question Asked 6 years, 11 months ago. Modified 6 years, 11 months ago. Viewed 55 times Are you sure it’s Python 3.4 you are using and not Python 2? – Lev Levitsky. Jul 10, 2015 at 19:48

Python: What does parenthesis () after a variable name mean?

Towards the bottom at the main loop, I’m seeing this line

But I have no idea what it does and I can’t even Google it. What is this?

The code below imports from task.py and project.py. But both files do not have anything related to result() hence I’m not including them here.

#!/usr/bin/env python3 from task import Task from project import Project main_menu = < 'title': 'MAIN MENU', 'items': ['1. Create a project', '2. Load a project', '3. Quit'], 'actions': < '3': exit, >> project_menu = < 'title': 'PROJECT MENU', 'items': ['1. Add a task', '2. Add task dependency', '3. Set task progress', '4. Show project', '5. Back to Main Menu'], 'actions': < '5': main_menu, >> def select_menu(menu): while True: print() print(menu['title']) #MAIN MENU print('\n'.join(menu['items'])) #1. create project, 2. load project .. selection = input('Select > ') next_action = menu['actions'].get(selection) #print(selection, menu['actions']) if next_action: return next_action else: print('\nPlease select from the menu') def create_project(): global cur_project global project_menu project_name = input('Enter the project name: ') cur_project = Project(project_name) return project_menu main_menu['actions']['1'] = create_project cur_menu = main_menu cur_project = None while True: result = select_menu(cur_menu) while callable(result): result = result() cur_menu = result 

select_menu returns an element of actions , which are all functions ( main_menu , exit , create_project . ). Thus, result is a function. result = result() will execute that function and replace the value in result with the return value of that function.

You have to see the global loop:

while callable(result): result = result() 

it just calls result function until it returns a non-function (probably a result), reassigning back the result name. result is just a name, it can reference anything including a function.

you can see that like traversing a tree node by node until you reach a leaf.

Python — Purpose of parentheses right after object’s and, Parentheses after a name means a function/method is called there. An object can be created by calling its constructor ( __init__ function). Constructor is invoked by calling the class itself as a function Workbook () The functions or object methods are called similarly using parentheses. Share Improve this …

How do parentheses work when printing a variable?

New to python (and coding in general) and was hoping for some help understanding this.

Here’s some sample code from Ipify:

from requests import get ip = get('https://api.ipify.org').text print('My public IP address is: <>'.format(ip)) 

I don’t really understand how the braces are working in second line, but I’ve tried writing it a few other ways that I understand instead:

ip = get('https://api.ipify.org').text print(f"my public IP is ") 

ip = get('https://api.ipify.org').text print("my public IP is", ip) 

My question is how is the code they provided in the first example better and what are the braces doing in their code?

Thanks in advance for any help.

Formatters work by putting in one or more replacement fields and placeholders defined by a pair of curly braces <>

str = "This code is written in <>" print(str.format("Python")) 

This code is written in Python 

Why is .format<> better than old Python 2 % ?

.format<> accepts tuple while % throws a TypeError

What does the comma «,» after a variable mean in Python?, It’s probably related to tuple but I don’t understand how, as the comma is supposed to be after the value and not the variable like i = 1, Thanks in advance for any clarification, EDIT: From the response suggested in comment by @Goralight. In Python, it’s the comma that makes something a tuple: >>> 1 1 >>> …

What are the parentheses for at the end of Python method names? [duplicate]

I’m a beginner to Python and programming in general. Right now, I’m having trouble understanding the function of empty parentheses at the end of method names, built-in or user-created. For example, if I write:

print "This string will now be uppercase".upper() 

. why is there an empty pair of parentheses after «upper?» Does it do anything? Is there a situation in which one would put something in there? Thanks!

Because without those you are only referencing the method object. With them you tell Python you wanted to call the method.

In Python, functions and methods are first-order objects. You can store the method for later use without calling it, for example:

>>> "This string will now be uppercase".upper >>> get_uppercase = "This string will now be uppercase".upper >>> get_uppercase() 'THIS STRING WILL NOW BE UPPERCASE' 

Here get_uppercase stores a reference to the bound str.upper method of your string. Only when we then add () after the reference is the method actually called.

That the method takes no arguments here makes no difference. You still need to tell Python to do the actual call.

The (. ) part then, is called a Call expression, listed explicitly as a separate type of expression in the Python documentation:

A call calls a callable object (e.g., a function ) with a possibly empty series of arguments .

the parentheses indicate that you want to call the method

upper() returns the value of the method applied to the string

if you simply say upper , then it returns a method, not the value you get when the method is applied

>>> print "This string will now be uppercase".upper >>> 

upper() is a command asking the upper method to run, while upper is a reference to the method itself. For example,

upper2 = 'Michael'.upper upper2() # does the same thing as 'Michael'.upper() ! 

What are the parentheses for at the end of Python, the parentheses indicate that you want to call the method upper () returns the value of the method applied to the string if you simply say upper, then it returns a method, not the value you get when the method is applied >>> print «This string will now be uppercase».upper >>> …

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