Functions, methods, and how many arguments do I have to give them?
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Why do the following lines give me the same result?
I tried to do the same with
list.append but got a
str type in python overloaded? How can this be achieved by writing a class/function? I would appreciate an example.
list.append takes two arguments - the list to modify and the element to append. So you need to do it like this:
ls =  list.append(ls, 2)
which is equivalent to the much more popular:
Parameters and Arguments, /arguments, and the C++ standard suggests that it should support at least 256 Most of the functions found in Excel require some input or information in order to calculate correctly. For example, to use the AVERAGE function, you need to give it a range of numbers to average. =AVERAGE(A1:A100) Any input you give to a function is called an argument. The basic construct of a function is: Function_Name(argument1, …
list.append are both functions.
str.upper takes one argument.
>>> str.upper('test') 'TEST'
list.append takes two arguments.
>>> my_list =  >>> list.append(my_list, 1) >>> my_list 
list.append (like other functions) are also non-data-descriptors with a
__get__ method which in this context has two implications:
- When you access the function through the class via the dot notation (
list.append) the function's
list.append.__get__) is called but it returns just the function itself.
- When you access the function through an instance (
my_list.append) the function's
__get__method is called and it will return a new callable acting like the original function, but with whatever was "in front of the dot" automatically passed as the first argument. .
That's why you need to pass 1 - 1 = 0 arguments when calling
my_string.upper() and 2 - 1 = 1 argument when calling
>>> 'my_string'.upper() 'MY_STRING' >>> >>> my_list =  >>> my_list.append(1) >>> my_list 
You could even get these modified callables (methods) by explicitly calling
__get__ and passing the argument to be bound (what has been before the dot) as its argument.
>>> my_string = 'my_string' >>> upper_maker = str.upper.__get__(my_string) >>> upper_maker() 'MY_STRING' >>> >>> my_list =  >>> appender = list.append.__get__(my_list) >>> appender(1) >>> my_list 
Finally, here's a short example demonstrating how descriptor instances can detect whether they are being accessed via their owner-class or via an instance.
class Descriptor: def __get__(self, instance, owner_class): if instance is None: print('accessed through class') # list.append.__get__ would return list.append here else: print('accessed through instance') # list.append.__get__ would build a new callable here # that takes one argument x and that internally calls # list.append(instance, x) class Class: attribute = Descriptor() Class.attribute # prints 'accessed through class' instance = Class() instance.attribute # prints 'accessed through instance'
Quoting Dave Kirbys answer from Relationship between string module and str:
There is some overlap between the string module and the str type, mainly for historical reasons. In early versions of Python str objects did not have methods, so all string manipulation was done with functions from the string module. When methods were added to the str type (in Python 1.5?) the functions were left in the string module for compatibility, but now just forward to the equivalent str method.
However the string module also contains constants and functions that are not methods on str, such as formatting, character translation etc.
How many maximum arguments can be passed to a function in C , As your programs grow in complexity, their Main() methods will contain many You will understand how to send data to these methods and receive information back from them. Depending on the method, there might be an argument within the Methods are similar to the procedures, functions, and subroutines used in Fill in the foo and bar functions so they can receive a variable amount of arguments (3 or more) The foo function must return the amount of extra arguments received. The bar must return True if the argument with the keyword magicnumber is worth 7, and False otherwise.
There is nothing at all magical going on with
str (except that we have a nice syntactic shortcut to creating one using ""). You can write a class that behaves like
list to see more clearly what is happening here.
class MyClass(): def __init__(self, arg): self.val=str(arg) def do_thing(self): self.val = "asdf" def do_thing_with_arg(self, arg): self.val = "asdf " + str(arg) def __repr__(self): return self.val my_thing = MyClass("qwerty") # this is like 'hello'.upper() my_thing.do_thing() print(my_thing) # it prints 'asdf' my_thing = MyClass("qwerty") # this is like str.upper('hello') MyClass.do_thing(my_thing) print(my_thing) # it prints 'asdf' my_thing = MyClass("qwerty") # this is like my_list.append('qwerty') my_thing.do_thing_with_arg('zxcv') print(my_thing) # it prints 'asdf zxcv' my_thing = MyClass("qwerty") # this is like list.append(my_list, 'qwerty') MyClass.do_thing_with_arg(my_thing, 'zxcv') print(my_thing) # it prints 'asdf zxcv'
The short version is, you're invoking what looks like an "instance method" on a class, but you are supplying the instance ('
self') yourself as the first argument to the function call.
Are there guidelines on how many parameters a function should , You can make up any names you want for the functions you create, except that The parameter list may be empty, or it may contain any number of parameters. Python Arbitrary Arguments. Sometimes, we do not know in advance the number of arguments that will be passed into a function. Python allows us to handle this kind of situation through function calls with an arbitrary number of arguments. In the function definition, we use an asterisk (*) before the parameter name to denote this kind of argument.
Microsoft Visual C#: An Introduction to Object-Oriented Programming, And also, how to pass arrays to such functions as parameters. Rest parameters A function can be called with any number of arguments, no matter how it is defined. three dots followed by the name of the array that will contain them. It does not support array methods, so we can't call arguments.map(. So why do we have both methods and functions in Python? The official answer is that there is a small difference between them. Namely: a method always belongs to an object (e.g. in the dog.append(4) method .append() needed the dog object to be applicable), while a function doesn’t necessarily. To make this answer even more twisted: a method is
3. Functions, You can use any data type for a parameter of a method or a constructor. You can use a construct called varargs to pass an arbitrary number of values to a It's a shortcut to creating an array manually (the previous method could have used The arguments object is a local variable available within all non-arrow functions. You can refer to a function's arguments inside that function by using its arguments object. It has entries for each argument the function was called with, with the first entry's index at 0. For example, if a function is passed 3 arguments, you can access them as
Rest parameters and spread syntax, That being said, though, you do need to keep it in mind and be sure it is how you want An Ajax request has a well-defined and specific life cycle, just like any HTTP request For instance, when the request begins, your function will be called. This method takes three parameters: the HTTP method to perform, the URL to There are two ways in which a method is called i.e., method returns a value or returning nothing (no return value). The process of method calling is simple. When a program invokes a method, the program control gets transferred to the called method.
- at which list you do expect to append 1?
- What would your
- What's the relation between your first example for upper cases and append an integer to a list?
- "How can this be achieved by writing a class/function?" How can what be achieved? It's not at all clear what you are asking for.
- This question is only trivial on the surface. +1
list.appendfall under the category of instance method under the
- @Idlehands It's a little word-thinky. If I had to try to be very correct, I would say:
list.appendare functions that return methods when their
__get__method is called with a non-
instanceargument - where I would define a method as a callable which partially (i.e. with bound first argument) applies a function defined inside a class.
- Thanks for the clarification, I was genuinely confused because my background is not in comp-sci so terminologies and paradigms are weak spots for me. My understanding was that any functions defined within a class (i.e. a dot preceding its name) is always a method (instance/class/static) hence my original question. In this case I figured
str.upperwould have been defined similar as
class str: def upper(self):where it either runs as
- @Idlehand The whole descriptor topic is hard. Rule of thumb when writing code:
my_class.function_namegives you a function to which you must pass all arguments.
instance_of_class.function_namegives you a method to which
instance_of_classis automatically passed as the first argument (usually named
- this is probably the best answer one can give here. Don't understand the -1. Well done.
- It probably got downvoted because it was literally a straight quote from another answer in a related thread.