If you call a Python script from a shell, the arguments are placed after the script name. The arguments are separated by spaces. Inside the script these arguments are accessible through the list variable sys. The name of the script is included in this list sys. The following script arguments. We will introduce now functions, which can take an arbitrary number of arguments. Some definitions, which are not really necessary for the following: A function with an arbitrary number of arguments is usually called a variadic function in computer science.
To use another special term: A variadic function is a function of indefinite arity. The arity of a function or an operation is the number of arguments or operands that the function or operation takes.
The term was derived from words like "unary", "binary", "ternary", all ending in "ary". The asterisk character has to precede a variable identifier in the parameter list. We learn from the previous example that the arguments passed to the function call of varpafu are collected in a tuple, which can be accessed as a "normal" variable x within the body of the function. If the function is called without any arguments, the value of x is an empty tuple. Sometimes, it's necessary to use positional parameters followed by an arbitrary number of parameters in a function definition.
This is possible, but the positional parameters always have to precede the arbitrary parameters. In the following example, we have a positional parameter "city", - the main location, - which always have to be given, followed by an arbitrary number of other locations:.
An argument will be unpacked and not packed. In other words, the elements of the list or tuple are singularized:. There is hardly any need to mention that this way of calling our function is more comfortable than the following one:.
Additionally, the previous call f p[0],p[1],p[2] doesn't work in the general case, i. There is also a mechanism for an arbitrary number of keyword parameters. You might ask yourself, why we used both a positional parameter "x" and the variable parameter " l" in our function definition.
This information is communicated to the compiler via a function prototype. A Prototype can occur at the top of a C source code file to describe what the function returns and what it takes return type and parameter list.
When this is the case occuring at the top of the file , the function prototype should be followed by a semi-colon. The function prototype is also used at the beginning of the code for the function. Thus the prototype can occur twice in a C source code file.
When the prototype occurs with the code NO semicolon is used. In C, the "main" function is treated the same as every function, it has a return type and in some cases accepts inputs via parameters. The only difference is that the main function is "called" by the operating system when the user runs the program. Thus the main function is always the first code executed when a program starts.
Every C function must specify the type of data that is being generated. For example, the max function above returns a value of type "double". Inside the function, the line "return X;" must be found, where X is a value or variable containing a value of the given type. When a line of code in a function that says: "return X;" is executed, the function "ends" and no more code in the function is executed. The value of X or the value in the variable represented by X becomes the result of the function.
When one piece of code invokes or calls a function, it is done by the following syntax:. The function name must match exactly the name of the function in the function prototype. The args are a list of values or variables containing values that are "passed" into the function. You can give a function expression a name.
Named function expressions allow a function expression to refer to itself, which is useful for self-recursion:. The following is a function declaration:. The preceding looks like a function expression, but it is a statement see Expressions Versus Statements. It is roughly equivalent to the following code:. In other words, a function declaration declares a new variable, creates a function object, and assigns it to the variable. The constructor Function evaluates JavaScript code stored in strings.
For example, the following code is equivalent to the previous example:. However, this way of defining a function is slow and keeps code in strings inaccessible to tools. Therefore, it is much better to use a function expression or a function declaration if possible. Evaluating Code Using new Function explains Function in more detail; it works similarly to eval.
Function declarations are completely hoisted. That allows you to call a function before it has been declared:. The reason the preceding code works is that JavaScript engines move the declaration of foo to the beginning of the scope. They execute the code as if it looked like this:. Therefore, using a var declaration and a function expression similarly to the previous example results in an error:.
Most JavaScript engines support the nonstandard property name for function objects. Function declarations have it:. The name of anonymous function expressions is the empty string:. The name of a function is useful for debugging. Some people always give their function expressions names for that reason.
Should you prefer a function declaration like the following? Or the equivalent combination of a var declaration plus a function expression? They are basically the same, but function declarations have two advantages over function expressions:.
They can supply a value for this when invoking a method and thus are mainly interesting in an object-oriented context see Calling Functions While Setting this: call , apply , and bind.
This section explains two use cases for nonmethods. This method uses the elements of argArray as arguments while calling the function func ; that is, the following two expressions are equivalent:.
It is not needed in a non-object-oriented setting and is thus null here. Thanks to apply , we can use Math. This performs partial function application —a new function is created that calls func with this set to thisValue and the following arguments: first arg1 until argN , and then the actual arguments of the new function. Here, we use bind to create a new function plus1 that is like add , but only requires the parameter y , because x is always Hence, the number of actual parameters and formal parameters can differ in two ways:.
The special variable arguments exists only inside functions including methods. It is an array-like object that holds all of the actual parameters of the current function call. The following code uses it:. It is array-like, but not an array. On one hand, it has a property length , and individual parameters can be read and written by index.
On the other hand, arguments is not an array, it is only similar to one. It has none of the array methods slice , forEach , etc. If you like GeeksforGeeks and would like to contribute, you can also write an article using write. See your article appearing on the GeeksforGeeks main page and help other Geeks.
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