I turned magic into building blocks

Learning goals

1. Understand the use of magic blocks – custom functions
2. Learn about the result feedback of magic blocks – custom function return values
3. Understand the raw material transfer of magic blocks – custom function pass parameters
4. Learn about the types of magic blocks – classes and objects

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If programming is magic, then I will make you understand the use of a magic wand. I will make you understand the use of magic wand. If programming is magic, the basic data types of the magic box list, dictionary, and basic data types of the magic box. “If the programming is the zero basis of magical can read the Python tutorial” – (5) I’m magic should have a sense of logic Article 6: “if the programming is the zero basis of magical can read the Python tutorial” – (6) lean more powerful magic This series of tutorials will be in the form of a “magical world”, welcome all of you support.

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1. Understand the building blocks in the magical world

1.1 Understand the writing of custom functions

When we write an ordering system, we often prompt the menu bar for the user to choose. If the user enters another page and needs a new menu prompt when returning to the first page, we need to output it again. Is that particularly troublesome? We can take a look at the following example:

print('Please select the food number you want to eat and go in and pay')
print('1. Kung Pao Chicken ')
print(2. Spicy Chicken Wings)
print('3. Sticky rice ')
print('3. Dumplings')
print('4. Shaxian Classic Three-piece set ')
print('5. Multifarious meatballs')

c=int(input('Please enter menu number:'))
if c:
	print('Connecting to pay... ')
	b=input('Any key returns... ')
	if b:
		print('Returning to... ')

print('Please select the food number you want to eat and go in and pay')
print('1. Kung Pao Chicken ')
print(2. Spicy Chicken Wings)
print('3. Sticky rice ')
print('3. Dumplings')
print('4. Shaxian Classic Three-piece set ')
print('5. Multifarious meatballs')
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The above examples are only used to simulate the situation, and the code is not used as a reference for the function. At the beginning of the code, the prompt menu content, the code is as follows:

print('Please select the food number you want to eat and go in and pay')
print('1. Kung Pao Chicken ')
print(2. Spicy Chicken Wings)
print('3. Sticky rice ')
print('3. Dumplings')
print('4. Shaxian Classic Three-piece set ')
print('5. Multifarious meatballs')
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Prompt content after receiving user input a value. User input value, where any value can be entered, to judge the writing of the code:

if c:
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The above code evaluates the C variable, as long as it is not empty, then any number will work. In Python, empty values are ultimately judged to be False and True if any. Then simulate the connection to the payment system, input a value at will for a long time and return after confirmation:

c=int(input('Please enter menu number:'))
if c:
	print('Connecting to pay... ')
	b=input('Any key returns... ')
	if b:
		print('Returning to... ')
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Then reprint the menu bar. This is obviously duplicate code for the menu bar, used twice; Does this code seem too cumbersome? It’s just visually difficult. But don’t worry, Python provides custom functions to solve this problem. A custom function represents a function block that can be defined by itself. This function block can be used repeatedly. This function block can be composed of multiple codes.

Now let’s define the menu bar as a custom function. The syntax for defining a custom function begins with def, followed by a space; A space followed by a string of characters indicates the name of the function block; Followed by a bunch of parentheses followed by a colon. The code is as follows:

def caidan() :
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The above code starts with def, which means I’m going to write a custom function, followed by the name caidan, followed by a bunch of parentheses, and terminated by a colon; Next, we need to write the function code inside the function. At this point, we need to have a uniform indentation format, at least one:

def caidan() :
	# here is the code for caidan
	# here is the code for caidan
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We can simply copy and paste the entire menu tip code into our custom caidan function:

def caidan() :
print('Please select the food number you want to eat and go in and pay')
print('1. Kung Pao Chicken ')
print(2. Spicy Chicken Wings)
print('3. Sticky rice ')
print('3. Dumplings')
print('4. Shaxian Classic Three-piece set ')
print('5. Multifarious meatballs')
Copy the code

Is that correct? Wrong! Remember that when you customize a function, you need to write the function and then indent the structure in the name of the function; So the correct way to write this code is as follows:

def caidan() :
	print('Please select the food number you want to eat and go in and pay')
	print('1. Kung Pao Chicken ')
	print(2. Spicy Chicken Wings)
	print('3. Sticky rice ')
	print('3. Dumplings')
	print('4. Shaxian Classic Three-piece set ')
	print('5. Multifarious meatballs')
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This is the custom function function has been written, so how to use it? Pretty simple, you remember how print works? Print and input are functions that come with the system; They are used by enclosing a pair of parentheses after the function name. Such as input (); We write our own functions to use the same method, the name of the function after a pair of parentheses to complete the use of custom functions, such as caidan(). Take a look at the full code for this section:

def caidan() :
    print('Please select the food number you want to eat and go in and pay')
    print('1. Kung Pao Chicken ')
    print(2. Spicy Chicken Wings)
    print('3. Sticky rice ')
    print('3. Dumplings')
    print('4. Shaxian Classic Three-piece set ')
    print('5. Multifarious meatballs')

caidan()
c=int(input('Please enter menu number:'))
if c:
	print('Connecting to pay... ')
	b=input('Any key returns... ')
	if b:
		print('Returning to... ')

print('Please select the food number you want to eat and go in and pay')
print('1. Kung Pao Chicken ')
print(2. Spicy Chicken Wings)
print('3. Sticky rice ')
print('3. Dumplings')
print('4. Shaxian Classic Three-piece set ')
print('5. Multifarious meatballs')
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The above code defines the custom caidan function in the header and writes functions in the caidan function. Caidan () = caidan() = caidan() = caidan() = caidan() = caidan();

print('Please select the food number you want to eat and go in and pay')
print('1. Kung Pao Chicken ')
print(2. Spicy Chicken Wings)
print('3. Sticky rice ')
print('3. Dumplings')
print('4. Shaxian Classic Three-piece set ')
print('5. Multifarious meatballs')
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The result of the code in the function should be displayed when the program is running:

If caidan() is used instead of caidan(), we can cancel the menu at the bottom of the code. The code is as follows:

def caidan() :
    print('Please select the food number you want to eat and go in and pay')
    print('1. Kung Pao Chicken ')
    print(2. Spicy Chicken Wings)
    print('3. Sticky rice ')
    print('3. Dumplings')
    print('4. Shaxian Classic Three-piece set ')
    print('5. Multifarious meatballs')

caidan()
c=int(input('Please enter menu number:'))
if c:
	print('Connecting to pay... ')
	b=input('Any key returns... ')
	if b:
		print('Returning to... ')

caidan()
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Running results:



The results are consistent, but with much less code, it looks cleaner.

1.2 Understanding custom functions with Parameters

def jiafa() :
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def jiafa(s1,s2) :
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print(s1+s2)
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def jiafa(s1,s2) :
	print(s1+s2)
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jiafa(1.10)
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def jiafa(s1,s2) :
	print(s1+s2)

jiafa(1.10)
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def jiafa(s1,s2) :
	print('The sum of two numbers equals:',s1+s2)

a=int(input('Enter a number :'))
b=int(input('Please enter another number :'))
jiafa(a,b)
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1.3 Learn about custom functions with return values

Now all of a sudden, I don’t want to output in the function, I just want to get the result, I want to output or not output according to the situation, so how do I implement this requirement? Very simple, we just return the evaluated value, so that our function does the calculation, not the output; Output or not according to the situation at that time, flexible use.

Return the last line of a custom function using return, followed by a space, followed by a value. The result is the value returned by return. For example, we modify the code in 1.2:

def jiafa(s1,s2) :
    return s1+s2
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Compared with the original program output less, more than a return, and return followed by a space, space followed by the expression of the addition of two variables; This expression is not a direct value, but don’t worry, the expression will eventually be automatically evaluated to a value that will be returned by return. It doesn’t matter if you don’t understand, we can write:

def jiafa(s1,s2) :
	r=s1+s2
    return r
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The variable r receives the value of the addition of S1 and s2 and returns the same value for r. So we can call a function in our code and assign the result that the function returns to a variable:

c=jiafa(a,b)
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After jiafa has run all the code in its function, it returns a value that will be given to the C variable. Print c:

print('The result of addition is:',c)
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Or, instead of using a variable to receive the output, use the return value of the function directly:

print('The result of addition is:',jiafa(a,b))
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The final code is as follows:

def jiafa(s1,s2) :
    return s1+s2

a=int(input('Enter a number :'))
b=int(input('Please enter another number :'))
print('The result of addition is:',jiafa(a,b))
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The running results are as follows:

Second, the summary