This question already has answers here:
What's the difference between an argument and a parameter?
(38 answers)
Closed last month.
So I'm still pretty new to Python and I am still confused about using a parameter vs an argument. For example, how would I write a function that accepts a string as an argument?
Generally when people say parameter/argument they mean the same thing, but the main difference between them is that the parameter is what is declared in the function, while an argument is what is passed through when calling the function.
def add(a, b):
return a+b
add(5, 4)
Here, the parameters are a and b, and the arguments being passed through are 5 and 4.
Since Python is a dynamically typed language, we do not need to declare the types of the parameters when declaring a function (unlike in other languages such as C). Thus, we can not control what exact type is passed through as an argument to the function. For example, in the above function, we could do add("hello", "hi").
This is where functions such as isinstance() are helpful because they can determine the type of an object. For example, if you do isinstance("hello", int), it will return False since "hello" is a string.
See the FAQ:
What is the difference between arguments and parameters?
Parameters are defined by the names that appear in a function definition, whereas arguments are the values actually passed to a function when calling it. Parameters define what types of arguments a function can accept. For example, given the function definition:
def func(foo, bar=None, **kwargs):
pass
foo, bar and kwargs are parameters of func. However, when calling func, for example:
func(42, bar=314, extra=somevar)
the values 42, 314, and somevar are arguments.
See also:
language-agnostic What's the difference between an argument and a parameter?
This answer is my favourite.
For defining a function that accepts a string, see TerryA's answer. I just want to mention that you can add type hints to help people using your function to tell what types it accepts, as well as what type it returns.
def greeting(name: str) -> str:
return 'Hello ' + name
In Programming lingo, arguments refers to the data you are passing to the function that is being called whereas the parameter is the name of the data and we use the parameter inside the function to refer it and do things with it.
for example:
def functionname(something):
do some stuff with {something}
functionname(abc)
in this case,
abc --> argument
something --> parameter
A parameter is the placeholder; an argument is what holds the place.
Parameters are conceptual; arguments are actual.
Parameters are the function-call signatures defined at compile-time; Arguments are the values passed at run-time.
Mnemonic: "Pee" for Placeholder Parameters, "Aeigh" for Actual Arguments.
Related
Let's consider
foo(arg1=123, arg2=None) and foo(arg1=123).
Tell me please, if these two ways are equivalent ?
No, the two given function signatures (and hence functions) are not equivalent.
In foo(arg1=123, arg2=None), you have two arguments -- arg1 and arg2, which can be used inside the function as local names. Note that, assigning a value of None to some name does not make it anything special/different as far as the assignment statements are concerned. It is in fact a common way to give a placeholder value for a variable that is not mandatory or may be an empty mutable object.
On the other hand, foo(arg1=123) has only one argument arg1, which is available on the function's local scope for use.
Edit:
If you have a function defined as foo(arg1, arg2), both arguments are mandatory (positional) arguments.
So, foo(arg1=21) will throw a TypeError as you have not provided arg2. Whereas, foo(arg1=21, arg2=None) will work just fine as you have provided values for both the arguments.
Edit2:
If you have a function defined as foo(arg1=None, arg2=None) (or something similar i.e. with default values), both arguments are optional (keyword) arguments. In that case, both of the mentioned definitions would be the same.
Suppose python supported function overloading, how would we define overloaded functions for adding two numbers and concatenating two strings?
I just want to know how do we assign a particular data type to a parameter in the function definition or will it depend on the arguments given in the function call.
Would it be like this:
def num(a=int,b=int):
return a+b
def strng(a=str,b=str):
return a+b
python is dynamically typed language. Hence, type checks are not strictly enforced. In defining a function, you can define an optional type for the parameters.
def function(a:int=0, b:int=0): return a + b
The type definition here really does nothing peculiar but probably helps with IDE autocompletion. You can pass in a string and you won't get any errors but it'll definitely throw an error when adding a number to a string.
This question already has answers here:
Order of Keyword and Non-Keyword Arguments
(2 answers)
Closed 7 years ago.
According to Python docs it is illegal to define a function as def test(a, b = 1, c): - any subsequent parameter to a parameter which has a default value (b = 1) also needs to be defined with a default value. The correct way would be def test(a, b = 1, c = 2):
Can someone explain it?
Edited: I think that having Polymorphism in title was confusing. Title has been changed to reflect the content of the question
When you define a default value for a parameter, it implicitly becomes optional in Python. This means that you don't need to call it with an explicit argument, the default argument is stored upon the time of the function's creation and is used whenever you don't supply an argument.
So in the case of test(a, b=1, c=2), you could pass in one argument(a), or two arguments (a and b) or three arguments (a, b, c). The Python compiler/interpreter will figure out which argument belongs to which parameter based on which arguments you pass in, and in the order that you passed them in (unless you use explicit keys for the optional arguments, then you can switch the order).
But now think, if the function were defined as test(a, b=1, c), how would the compiler/interpreter figure out what a call like test(x, y) does? x is obvious, it's an argument to a. But for y, is it an argument to c (which would be required, but then y is being passed in as the second parameter which makes no sense since we're skipping b), or an implicit argument to b (which doesn't make sense since then c is a required parameter with no argument)?
As you can see, this call makes no sense either way, so Python requires that all required parameters be bundled together as the first arguments to the call to avoid confusion.
I am a beginner in python programming and recently i came across functions,parameters,arguments and...
I have done a lot of research on Parameters and Arguments(Even checked the answers of similar past questions on StackOverflow)but i couldn't get their meanings.
Some say,parameters are variables which we give them to functions while we are defining them and arguments are values that are passed in function once we given them to the function in order to run the function.While some other say no,it's not like that.Parameters and Arguments are same and do the same task...
Can anyone tell me the meaning Parameters and Arguments in a clear way?
Are Parameters and Arguments considered variables?
For what kind of purpose do we use them?
Please don't explain too much complicated,i am a beginner.
Thank you so much.
Per the official documentation:
Parameters are defined by the names that appear in a function definition, whereas arguments are the values actually passed to a function when calling it. Parameters define what types of arguments a function can accept. For example, given the function definition:
def func(foo, bar=None, **kwargs):
pass
foo, bar and kwargs are parameters of func. However, when calling func, for example:
func(42, bar=314, extra=somevar)
the values 42, 314, and somevar are arguments.
The glossary defines them as:
Argument: A value passed to a function (or method) when calling the function.
Parameter: A named entity in a function (or method) definition that specifies an argument (or in some cases, arguments) that the function can accept.
Python doesn't really have "variables" like some other languages - it has "names" referring to "objects". See e.g. "Code like a Pythonista" and "Facts and myths about Python names and values".
Take it this way:
Parameter:
A parameter represents a value that the procedure expects you to pass when you call it. The procedure's declaration defines its parameters.
Argument:
An argument represents the value that you pass to a procedure parameter when you call the procedure. The calling code supplies the arguments when it calls the procedure.
Example:
int add (int value1, int value2) // Here value1 and value2 are PARAMETERS.
{
return value1+value2;
}
Now while calling the function
answer = add(2,3); // Here values 2 and 3 are ARGUMENTS.
Same goes with Python, while declaration, they are parameters, while calling they are arguments.
Some may differ with what i have written, but this is how it is actually known in programming world.
While I'm going through Python code and seeing functions called, I notice things like
functionCall(argument='something')
or
someclass.functionCall(argument='something')
I've played around with it and noticed you have to name that variable with the same name as the one in the scope of the function or class function itself. Is that just a convention (for useful naming) or is there more to it that I'm missing?
Those are just standard keyword arguments.
They are mainly useful when calling functions that usually assume default values, but the user is interested in passing a custom value without affecting the other defaults.
For example:
def foo(a='a', b='b', c='c'):
print a + b + c
Then:
>>> foo()
'abc'
>>> foo(c='x') # don't know or care about a and b's value
'abx'
This is called a keyword argument. Keyword arguments have a couple distinct advantages:
They can be specified in any order by the caller.
They have default values, which means the caller doesn't have to provide a value for each argument if the defaults are sensible.
They can make code more readable. For example, foo(width=100, height=200) is easier to understand than foo(100, 200). It is also easier to use, because you don't have to remember whether the function takes width,height or height,width.
It is good to have named arguments as arguments can be specified in any order by using named arguments.
Even required arguments (like object, which has no default value) can be named, and named arguments can appear in any order.
Also see This
Python's argument passing mechanisms are extremely flexible.
cons: too many arguments to a function. Solutions: split into multiple functions, pass some args together in a dictionary or object.
cons: bad variable names. Solution: give variables more descriptive names.
Or remember the correct order .. :)
class xyz:
def __init__ (self, a='1', b='2'):
print a,b
xyz(b=3,a=4)
xyz(a=5,b=6)
>>4 3
>>5 6
these are keyword parameters. They enable you to pass parameters in any order (useful for skipping optional parameters)
Please note though, calling functions that way comes with a little bit of overhead:
def test(a,b,c):
return a+b+c
def t1():
return test(1,2,3)
def t2():
return test(a=1, b=2, c=3)
timeit(t1)
0.23918700218200684
timeit(t2)
0.2716050148010254