Python learning notes

Introduction

This is a memo of what I learned for studying python. Please point out any errors.

Built-in functions

python

#Type conversion
#Convert to int
int("100")     #Decimal number
int("100", 2)  #Binary number
int("100", 16) #Hexadecimal
#Convert to float value
float()
#Convert to string
str()
#Character output
print("String")
print("String"+"String2")  # Stringを連結する
print("String"+ str(100)) #Convert numbers to letters and concatenate
print("String",100)       #Letter and number concatenation(There is a space in between)
#Character input
test = input()

#total
list = [1,2,3]
sum(list) #result: 6

#Maximum value
max(list) #result: 3

#minimum value
min(list) #result: 1

#length
len(list) #result: 3

for statement

python

loop = [0,1,2,3]

#Loop for the number of arrays
for i in loop:
    #Loop contents

#Loop for the specified number of times
for i in range(5):
    #Loop contents

#Loop in a specific range
for i in range(2,4):
    #Loop contents

while statement

cnt = 1
while cnt <= 10:
   print(cnt)
   cnt = cnt + 1 #Count addition

Loop control

How to use the else statement

else is executed after the loop ends. However, if the break statement breaks the loop, else will not be executed.

Class=["Tanaka","Suzuki","Sato"]
check ="Tanaka"
#Check if "Yamada" is in the class name
for name in Class:
   if check == name:
      print(name+"Is a classmate")
      break
else:
   print(check +"Is not a classmate")

if statement

python

testA = 1

if 1 == test:
    #Processing at True
else:
    #Processing when false

testB = "TEST"
if "T" in testB:
    #Processing at True
elif "B" in testB:
    #Processing when true

operator

Comparison operator

Logical operator

A < B and B < C In such a case, you can also write as follows A < B < C

Bit operator

function

def Name1():
  #Function processing
  return 0

#Define default arguments
def Name1():
  #Function processing
  return 0

#Define default arguments
def Name2(name="Anonymous"):
 print( "What's your name" + name + "is" )

#Define default arguments
def NameAndAge(name="Anonymous", age=25):
 print( "What's your name" + name + "is" )
 print( "How old are you" , age,"I'm talented" )
    

#Specify keywords
NameAndAge(age=12, name="Taro")

module

import random                 #Load the module
import random as rm           #Specify a name for the module
from statistics import median #Load the function in the module
from statistics import *      #Load all functions in the module

Built-in data type

Numeric type

XX base notation

String type

Replace / delete

test = "ABCDE"
test2 = test.replace("B","O")  #Replace B with O
test3 = test.replace("B","")   #Delete B
#However, the original variable does not change
test   # "ABCDE"
test2  # "AOCDE"
test3  # "ACDE"

Split / concatenate

test = "1 2 3 4 5"

#Divide by space
test_split = test.split(" ")
#[.]With test_Concatenate split data
test_join = ".".join(test_split ) 

test          # "1 2 3 4 5"
test_split    # ["1","2","3","4","5"]
test_join     # "1.2.3.4.5"

Other methods

format

Insert a string using format

test= "my name is{}is"
test.format("Taro")                 # 私の名前はTaroです

#Specify the order
test ="His name is{0}is.{0}Age{1}才is."
test.format("Jiro","25")            # 彼の名前はJiroです。Jiroの年齢は25才です。

#Specify keywords
test ="His name is{Name}is.{Name}Age{Age}才is."
test.format(Name="Jiro",Age="25")   # 彼の名前はJiroです。Jiroの年齢は25才です。

#Specify in the dictionary
test = "{0[name]}Is{0[age]}I'm talented"
dictionary = {'name':'Taro' , 'age':'14'}
test.format(dictionary)            #Taro is 14 years old

#Specify notation
test = "my name is{:>10}is"       #Right justified
test.format("Taro")                # 私の名前は     Taroです

test = "{:.1%}"
test.format(0.25)                   # 25.0%

#Display as f character string(python3.6 or later)
name="Taro"
f"my name is{name}is"

Escape character

raw string

If r is added, the character is displayed as it is.

raw = r"c:\Users\XX\Document"

bool type

Get True or False values

sequence

Refers to the one in which multiple elements are arranged in order.

• String type (str type, bytes type) is also a member of the sequence Dictionary types and set types are not included in the sequence because there is no concept of order.

list

python

#List declaration
list = [1,2,3]
list2= [2,3,4]

#List concatenation
list3 = list + list2
list3 #result: [1,2,3,2,3,4]

#Specify the beginning
list[0] = 0
list #result: [0,2,3]

#Specify the end
list[-1] = 1
list #result: [0,2,1]

#Slice specification
slice = [0,1,2,3,4,5]
slice[1:3] # [1,2]
slice[:4]  # [0, 1, 2, 3]
slice[3:]  # [3, 4, 5]
#Specify an even number
slice[::2] # [0,2,4] 
#Replace with slice
slice[1:2] = [10,11]
slice      # [0, 'a', 'b', 2, 3, 4, 5]
#Delete with slice
slice = [0,1,2,3,4,5]
del slice[4:]
slice      # [0, 1, 2, 3]

#Delete element
list = [0,1,2]
del list[2]
list #result: [0,1]

#Sorting elements(ascending order)
list = [3,5,2,1,0]
list.sort()
list    # [0, 1, 2, 3, 5]

#Sorting elements(descending order)
list = [3,5,2,1,0]
list.sort(reverse=True)
list    # [5, 3, 2, 1, 0]

#Customize the sort
#Sort in descending order of the sum of the numbers in the array
def sumAll(num):
   #Sum and return the numbers in the array
   return num[0] + num[1] + num[2]

list = [[10, 50, 30],[20, 50, 40],[80, 60, 70]]
list.sort(key=sumAll, reverse=True)
list # [[80, 60, 70], [20, 50, 40], [10, 50, 30]]

Tuple

Tuples look a lot like lists, but you can't change the elements.

#Tuple declaration
Months =("Jan","Feb","Mar","Apr","May","Jun","Jul")
#Or
Months ="Jan","Feb","Mar","Apr","May","Jun","Jul"

#When there is one element, put a comma at the end
Day= ("Mon",)
#Connection is OK
Months = Months + ("Aug","Sep","Oct","Nov","Dec")

#Unpack assignment
a = 1
b = 2
a , b = b , a
a     # 2
b     # 1

Use as a key

Tuples are sequences that cannot be changed, so dictionary keys and Can be an element of set

#Register your birthday in the dictionary
birthdays = {("April","1 day"):"Yamada Taro",
            ("June","The 6th"):"Hanako Yamada",
            ("November","11th"):"Jiro Yamada"}
#Specify date
birthday =("June","The 6th")
#Find a matching key in the for statement
for day in birthdays:
    if birthday == day:
        print(birthdays[day]) #Hanako Yamada
        break

set Data used to manage non-overlapping elements

test1 = {1,2,3}
test2 = {3,4,5}

#Union
test1 | test2                # {1, 2, 3, 4, 5}
test1.union(test2)           # {1, 2, 3, 4, 5}

#Difference set
test1 - test2                # {1, 2}
test1.difference(test2)      # {1, 2}
#Logical AND
test1 & test2                # {3}
test1.intersection(test2)    # {3}

#Exclusive OR
test1 ^ test2                     # {1, 2, 4, 5}
test1.symmetric_difference(test2) # {1, 2, 4, 5}

#Convert from list to set
list = [1,2,3,4,5]
set(list)                    # {1, 2, 3, 4, 5}
#Comparison
testA = {1,2,3,4,5,6}
testB = {3,4,5}
Check = testA & testB

if 4 in Check:
    print("4 is included in Test A and Test B")
if {3,4} <= Check:
    print("3,4 is included in Test A and Test B")

Dictionary (dictionary)

Manage the array by associating Key and Value

#Define dictionary type
test = { "name": "Taro",
         "age": "25"
         "Birthplace": "Tokyo"}

# dict()Defined using
dict([['key1','value1'],['key2','value2']])  # {'key1': 'value1', 'key2': 'value2'}
dict(key1='value1', key2='value2')           # {'key1': 'value1', 'key2': 'value2'}

#to add
test ={'name':'Taro'}      # {'name': 'Taro'}
test["sex"] ="Man"
test                       # {'name': 'Taro', 'sex': 'Man'}

#Combine with update method
test = {'name': 'Taro', 'sex': 'Man'}
test.update({'sex':'woman','age':'12 years old'})
test # {'name': 'Taro', 'sex': 'woman', 'age': '12 years old'}


#delete
test = {'name': 'Taro', 'sex': 'Man'}
del test["sex"]
test                       # {'name': 'Taro'}

#Check the existence of the element and add the element
test = {'name':'Goro','age':'12'}
word = "age"
if word in test:
    #Exists
   test[word] = test[word]+'Talent'
else:
    #not exist
    test[word] = 'Blank'
test

#Add elements using get
test = {'name':'Goro'}
word = "age"

test[word] = test.get(word, 'Blank')
test                   # {'name': 'Goro', 'age': 'Blank'}

Changeable / Not possible Data

comment

#At the beginning of the comment#Put on

docstring Add a description of the function using docstring

def docstring():
    '''
docstring test
Test 1
Test 2
Test 3
    '''
    Test = "ran docstring"
    print(Test)
    
print(docstring.__doc__)   #Get the explanation of docstring as a string
help(docstring)            #Check the explanation of the function from help