Python basics: functions

Functions, built-in functions

Function: A definition of a group of programs

Built-in functions: Functions preset in python itself

Think of it as a program version of a variable

Method

A method is a method that performs processing on a specific value.

Method

value.Method name()

Instance method

There is also an instance variable that retrieves value elements and so on. Instance variables have no arguments because they are variables, not functions.

Instance variables

value.Instance variable name

Taking append as an example, it is as follows.

append

# append()Is a method to use if you want to add only one new element to the list.

al = ["1","2","3","4","5"]
al.append("f")
print(al) 
# ["1","2","3","4","5","f"]Is output

String method

A method for enlarging and counting characters.

city = "Nagoya"
print(city.upper()) 
#output: 「NAGOYA」

print(city.count("N")) 
#output: 「1」

print("I{}birth,{}Birthplace".format("Aichi", "Nagoya"))
#output:"I was born in Aichi and from Nagoya"
#Where to embed{}Specified by. The argument does not have to be a string type

# {}The value to be inserted in can be specified in the insertion order and the same value can be repeated.

print("I{1}birth,{0}Growing up{1}Citizen".format("Aichi", "Nagoya"))
#output:"I was born in Nagoya, raised in Aichi, and a citizen of Nagoya"

List type method

index()
#Method to find out if it is in the index number

count()
#Some methods to output

al = ["0", "1", "2", "3", "3"]
print(al.index("0")) 
#output: 「0」
print(al.count("3")) 
#output: 「2」

sort()
#This will sort the list in ascending order.

reverse()
#Reverse the order of the elements in the list

#  sort()And reverse()The contents of the list are changed directly.
#There is no return value, so print(list.sort())Even if None is returned

soted()
#Built-in function sorted()And the original value remains the same

# sort()Usage example

list = [1, 3, 2, 4]
list.sort()
print(list) # [1, 2, 3, 4]It will be displayed.

# reverse()Usage example

list = ["Or", "Ki", "Ku", "Ke", "This"]
list.reverse()
print(list) 
#output: ["This", "Ke", "Ku", "Ki", "Or"]

function

"Def function name(): 」

def eat():
    print ("eat")

#Clarify the scope of processing with indentation
#The function call is "function name"()Will be

eat() 
 #output:eat

argument

If you set an argument, You can use that value in a function

def function name(argument):

def ii(n):
    print(n + "is")

ii("yellow")
#output:is yellow
#If you specify the argument as a variable, you can change the output result each time.

def ii(n):
    print(n + "is")

name = "yellow"
ii(name) 
#is yellow

name = "black"
ii(name) 
#output: black
#Variables defined in the function,Arguments can only be used within a function

Multiple arguments

Arguments separated by commas Specify more than one

def ii(sei, name):
    print("Last name is" + sei + "And the name is" + name + "is.")

ii("j", "bb") 
#"Last name is j and first name is bb." Is output.

Initial value of argument

When you set the initial (default) value If left blank, the initial value is automatically set. Argument = set in the form of initial value

def ii(family="j", first="bb"):
    print("Last name is" + family + "And the name is" + first + "is.")


ii("b")
#"Last name is b and first name is bb." Is output.
#If you want to pass only the first argument, ii(first="cc")Designated as

#In addition, it is necessary to always set the initial value in the argument after the argument for which the initial value is set.
#Therefore, it is possible to set the initial value only for the last argument as follows.

def ii(family, first="aa"):
    print("Last name is" + family + "And the name is"+ first + "is.")
#When only the previous argument is set, an error will occur if it is not set in the latter argument.

def ii(family="zz", first):
    print("Last name is" + family + "And the name is" + first + "is.")

return

Variables and arguments defined in a function cannot be used outside the function return allows you to pass the return value to the caller of the function

def ii(family = "jj", first = "bb"):
    comment = "Last name is" + family + "And the name is" + first + "is."

print(ii("ss")) 
#None is output

def ii(family = "jj", first = "bb"):
    comment = "Last name is" + family + "And the name is" + first + "is."
    return comment #Pass the return value to the function

print(ii("ss")) 
#"Last name is ss and first name is bb." Is output.