Jak volat funkci v Python (Příklad)

V čem je Funkce Python?

A Funkce v Python is a piece of code which runs when it is referenced. It is used to utilize the code in more than one place in a program. It is also called a method or a procedure. Python provides many inbuilt functions like print(), input(), compile(), and exec(), but it also gives you the freedom to create your own functions.

Jak definovat a volat funkci v Python

Funkce v Python is defined by the “def” statement followed by the function name and parentheses ( () ).

Příklad:

Let us define a function by using the command “def func1():” and call the function. The output of the function will be “I am learning Python funkce".

The function call func1() invokes our def func1(): and prints the command “I am learning Python function None.”

There is a set of rules in Python programování definovat funkci.

• Any arguments or input parameters should be placed within these parentheses.
• The function first statement can be an optional statement — the docstring or documentation string of the function.
• The code within every function starts with a colon (:) and should be indented (space).
• The statement return (expression) exits a function, optionally passing back a value to the caller. A return statement with no arguments is the same as return None.

Význam odsazení (mezera) v Python

Before we get familiar with Python funkcí, je důležité, abychom rozuměli pravidlu odsazení, které se má deklarovat Python functions, and these rules are applicable to other elements of Python as well, such as declaring conditions, loops, or variables.

Python follows a particular style of indentation to define the code. Since Python functions do not have any explicit begin or end like curly braces to indicate the start and stop of the function, they have to rely on this indentation. Here we take a simple example with the “print” command. When we write the “print” function right below the def func1(): line, it will show an “indentation error: expected an indented block”.

Now, when you add the indent (space) in front of the “print” function, it should print as expected.

At least one indent is enough to make your code work successfully. But as a best practice, it is advisable to leave about 3–4 spaces of indent to call your function.

It is also necessary that while declaring indentation, you maintain the same indent for the rest of your code. For example, in the below screenshot, when we call another statement “still in func1” and it is not declared right below the first print statement, it will show an indentation error: “unindent does not match any other indentation level.”

Now, when we apply the same indentation for both the statements and align them on the same line, it gives the expected output.

Jak funkce vrátí hodnotu?

The return command in Python specifies what value to give back to the caller of the function. Let us understand this with the following example.

Krok 1) Funkce nic nevrací

Here we see when a function does not “return”. For example, we want the square of 4, and it should give the answer “16” when the code is executed. It gives that when we simply use the “print x*x” code, but when you call the function “print square” it gives “None” as an output. This is because when you call the function, recursion does not happen and it falls off the end of the function. Python returns “None” for falling off the end of the function.

Step 2) Replace the print command with an assignment command

To make this clearer, we replace the print command with an assignment command. Let us check the output.

When you run the command “print square (4)”, it actually returns the value of the object. Since we do not have any specific function to run over here, it returns “None”.

Step 3) Use the ‘return’ function and execute the code

Now, here we will see how to retrieve the output using the “return” command. When you use the “return” function and execute the code, it will give the output “16.”

Krok 4) Spusťte příkaz 'print square'

Funkce v Python jsou samy o sobě objektem a objekt má nějakou hodnotu. Zde uvidíme jak Python treats an object. When you run the command “print square”, it returns the value of the object. Since we have not passed any argument, we do not have any specific function to run over here, so it returns a default value (0x021B2D30) which is the location of the object. In a practical Python program, you probably will not ever need to do this.

Argumenty ve funkcích

An argument is a value that is passed to the function when it is called.

In other words, on the calling side it is an argument, and on the function side it is a parameter.

Podívejme se jak Python arguments work.

Krok 1) Arguments are declared in the function definition. While calling the function, you can pass the values for those arguments as shown below.

Krok 2) To declare a default value for an argument, assign it a value at the function definition.

Příklad: x has no default value. The default value of y=0. When we supply only one argument while calling the multiply function, Python přiřadí zadanou hodnotu x, zatímco keeping the value of y=0. Hence the multiply of x*y=0.

Krok 3) This time we will change the value to y=2 instead of the default value y=0, and it will return the output as (4×2)=8.

Krok 4) You can also change the order in which the arguments are passed in Python. Here we have reversed the order of the values x and y to x=4 and y=2.

Krok 5) Multiple arguments can also be passed as an array. Here in the example we call the multiple args (1,2,3,4,5) by calling the (*args) function.

Příklad: We declared multiple args as the numbers (1,2,3,4,5); when we call the (*args) function, it prints out the output as (1,2,3,4,5).

Tip:

• In Python 2.7, function overloading is not supported. Function overloading is the ability to create multiple methods of the same name with a different implementation. Function overloading is fully supported in Python 3.
• There is quite a confusion between methods and functions. Methods in Python are associated with object instances, while functions are not. When Python volá metodu, sváže první parametr tohoto volání s odkazem na příslušný objekt. Jednoduše řečeno, samostatná funkce v Python je „funkce“, zatímco funkce, která je atributem třídy nebo instance, je „metodou“.

Zde je kompletní Python 3 kód

#define a function
def func1():
   print ("I am learning Python function")
   print ("still in func1")
   
func1()

def square(x):
  	return x*x
print(square(4))

def multiply(x,y=0):
	print("value of x=",x)
	print("value of y=",y)
    
	return x*y
  
print(multiply(y=2,x=4))

Zde je kompletní Python 2 kód

#define a function
def func1():
   print " I am learning Python function"
   print " still in func1"
   
func1()

def square(x):
  	return x*x
print square(4)

def multiply(x,y=0):
	print"value of x=",x
	print"value of y=",y
    
	return x*y
  
print multiply(y=2,x=4)

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