How do we define function test with arbitrary number of keywords as argument?
Sometimes when you write a function, it's not possible to know ahead of time how many arguments you will be providing to the function. Suppose we wish to write a function which will examine an arbitrary number of strings, and return the length of the longest string. (An alternative would be to write a function which accepts a list of values instead of individual arguments, but we'll continue this approach to illustrate the idea of a function with an arbitrary number of arguments.) By providing a function argument whose name begins with an asterisk, Python will collect any unnamed arguments passed to the function in a tuple, which can be accessed by the argument's name. To write a function which returns the length of the longest of a variable number of arguments, we can use this feature by including an argument whose name begins with an asterisk (in this case, we'll use the name *strings), which will become a tuple containing all the arguments passed to the function: Show
def longlen(*strings): max = 0 for s in strings: if len(s) > max: max = len(s) return maxNotice that inside the function, strings is just an ordinary tuple; the asterisk before its name is only needed when the function is defined. If we call the function with a collection of strings as arguments, it will check them all, and return the maximum length of any of them: >>> longlen('apple','banana','cantaloupe','cherry') 10 A similar technique can be used to create functions which can deal with an unlimited number of keyword/argument pairs. If an argument to a function is preceded by two asterisks, then inside the function, Python will collect all keyword/argument pairs which were not explicitly declared as arguments into a dictionary. When such an argument is used, it must be the last argument in the definition of the function. In this way, you can write a function to accept any named parameter, even if its name is not known when you are writing the function. To illustrate, consider a trivial function which simply gathers all the keyword/value pairs which were not explicitly declared in the function definition into a dictionary called dict, and then prints the value of each declared argument. Two named arguments are provided before the final argument to show how Python deals with named arguments in the presence of an argument with two asterisks. def printargs(a,b,**dict): print 'a=%s' % a print 'b=%s for k in dict.keys(): print '%s=%s' % (k,dict[k])We can test the function as follows: >>> printargs(x='seven',a='six',b='five',next='four',last='three') a=six b=five next=four x=seven last=threeNotice that arguments a and b were not placed in the dictionary, since they were explicitly specified as part of the function definition. In more complex situations, both kinds of special arguments (single and double asterisks) can be used in the same function. Once again, a trivial program will illustrate how this works: This article explains Python’s various function arguments with clear examples of how to use them. But before learning all function arguments in detail, first, understand the use of argument or parameter in the function. Also, See
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What is a function argument?When we define and call a Python function, the term parameter and argument is used to pass information to the function.
Example: In this example, the function 2 is defined with three parameters, 3, 4, 5, and print the sum of all three values of the arguments passed during a function call.
Output: Total is: 120function argument and parameter Note: A function must be called with the correct number of arguments by default. For example, the above function expects 3 arguments, so you have to call the 6 function with 3 arguments; otherwise, you will get an error.Does function need arguments? It is not mandatory to use arguments in function definition. But if you need to process user data, you need arguments in the function definition to accept that data. Also, we use argument in function definition when we need to perform the same task multiple times with different data. Can a function be called without arguments? If the function is defined with parameters, the arguments passed must match one of the arguments the function accepts when calling. Types of function argumentsThere are various ways to use arguments in a function. In Python, we have the following 4 types of function arguments.
Default ArgumentsIn a function, arguments can have default values. We assign default values to the argument using the ‘=’ (assignment) operator at the time of function definition. You can define a function with any number of default arguments. The default value of an argument will be used inside a function if we do not pass a value to that argument at the time of the function call. Due to this, the default arguments become optional during the function call. It overrides the default value if we provide a value to the default arguments during function calls. Let us understand this with an example. Example: Let’s define a function 9 with four arguments 0, 1, 2, and 3. In this function, 2 and 3 are default arguments with default values.
Passing one of the default arguments: If you pass values of the 2 and 3 arguments while calling a function, then those values are used instead of default values.Example:
Output: Student Details: Kelly 12 Six ABC School Student Details: Jessa 12 Seven XYZ School Keyword ArgumentsUsually, at the time of the function call, values get assigned to the arguments according to their position. So we must pass values in the same sequence defined in a function definition. For example, when we call Student Details: Kelly 12 Six ABC School Student Details: Jessa 12 Seven XYZ School4, the value “Jon” gets assigned to the argument name, and similarly, 12 to 1 and so on as per the sequence.We can alter this behavior using a keyword argument. Keyword arguments are those arguments where values get assigned to the arguments by their keyword (name) when the function is called. It is preceded by the variable name and an ( Student Details: Kelly 12 Six ABC School Student Details: Jessa 12 Seven XYZ School6) assignment operator. The Keyword Argument is also called a named argument. Example:
Output: Student Details: Jessa 14 Student Details: Jon 12 Student Details: Donald 13 Change the sequence of keyword arguments Also, you can change the sequence of keyword arguments by using their name in function calls. Python allows functions to be called using keyword arguments. But all the keyword arguments should match the parameters in the function definition. When we call functions in this way, the order (position) of the arguments can be changed. Example:
Positional ArgumentsPositional arguments are those arguments where values get assigned to the arguments by their position when the function is called. For example, the 1st positional argument must be 1st when the function is called. The 2nd positional argument needs to be 2nd when the function is called, etc. By default, Python functions are called using the positional arguments. Example: Program to subtract 2 numbers using positional arguments.
Note: If you try to pass more arguments, you will get an error.
Output Total is: 1200 Note: In the positional argument number and position of arguments must be matched. If we change the order, then the result may change. Also, If we change the number of arguments, we will get an error. Important points to remember about function argumentPoint 1: Default arguments should follow non-default arguments Example: Total is: 1201 Point: Default arguments must follow the default argument in a function definition Default arguments must follow the default argument. For example, When you use the default argument in a definition, all the arguments to their right must also have default values. Otherwise, you’ll get an error. Example: Total is: 1202 Point 2: keyword arguments should follow positional arguments only. we can mix positional arguments with keyword arguments during a function call. But, a keyword argument must always be after a non-keyword argument (positional argument). Else, you’ll get an error. I.e., avoid using keyword argument before positional argument. Example: Total is: 1203 Point 3: The order of keyword arguments is not important, but All the keyword arguments passed must match one of the arguments accepted by the function. Example: Total is: 1204 Point 4: No argument should receive a value more than once Total is: 1205 Variable-length argumentsIn Python, sometimes, there is a situation where we need to pass multiple arguments to the function. Such types of arguments are called arbitrary arguments or variable-length arguments. We use variable-length arguments if we don’t know the number of arguments needed for the function in advance. Types of Arbitrary Arguments:
The *args and **kwargs allow you to pass multiple positional arguments or keyword arguments to a function. Arbitrary positional arguments (# function with 2 keyword arguments grade and school def student(name, age, grade="Five", school="ABC School"): print('Student Details:', name, age, grade, school) # without passing grade and school # Passing only the mandatory arguments student('Jon', 12) # Output: Student Details: Jon 12 Five ABC School7)We can declare a variable-length argument with the 0 (asterisk) symbol. Place an asterisk ( 0) before a parameter in the function definition to define an arbitrary positional argument.we can pass multiple arguments to the function. Internally all these values are represented in the form of a tuple. Let’s understand the use of variable-length arguments with an example. This is a simple function that takes three arguments and returns their average: Total is: 1206 This function works, but it’s limited to only three arguments. What if you need to calculate the average marks of more than three subjects or the number of subjects is determined only at runtime? In such cases, it is advisable to use the variable-length of positional arguments to write a function that could calculate the average of all subjects no matter how many there are. Example: Total is: 1207 Output: Total is: 1208 Note: args is just a name. You can choose any name that you prefer, such as *subjects. Total is: 1209 Arbitrary keyword arguments (**kwargs)We saw how to use 7. Now let’s see how to use the 8 argument. The **kwargs allow you to pass multiple keyword arguments to a function. Use the 8 if you want to handle named arguments in a function.Use the unpacking operator( 5) to define variable-length keyword arguments. Keyword arguments passed to a kwargs are accessed using key-value pair (same as accessing a dictionary in Python).
How would you define a function with arbitrary keyword arguments?If you need to write a function that accepts arbitrary keyword arguments, you can use the ** operator in your function definition.
What keyword is used to define a function with variable number of input arguments?varargin is an input variable in a function definition statement that enables the function to accept any number of input arguments. Specify varargin by using lowercase characters. After any explicitly declared inputs, include varargin as the last input argument .
What is arbitrary number of arguments?The arbitrary arguments are passed as tuple (with one asterisk*) to the function, (you can change it to a list as shown in the code) and calculate the sum of its elements, by coding yourself using a for loop; if don't want to use the sum() method of python.
What is arbitrary keyword argument in Python?Arbitrary Keyword Arguments, **kwargs
If you do not know how many keyword arguments that will be passed into your function, add two asterisk: ** before the parameter name in the function definition.
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