Various processing of Python

A memorandum for myself

While coding using Python, I will leave what I searched for as "Oh, how do I do this process" in this post as a memorandum for myself. Will be updated from time to time.

Manipulation of dictionary type data (dict: dictionary type data to be operated)

Key-only list, value-only list

dict.keys()
dict.values()

By the way, a list that includes both keys and values

dict.items()

Add new keys and values

dict[New key] =value

Change the value corresponding to the key

dict[Key] =value
dict[Key] += 1

Specify a key to delete a dictionary element

del dict[Key]

List type data (list: list type data to be operated)

Determine if it has an element (returns True or False)

An element in list

Get the index of an element in the list

list.index(An element)

Add and insert elements in the list

list.append(An element) # リストの末尾にAn elementを追加
list.insert(0,An element) #Add the element at the top of the list (change 0 to insert the element at the corresponding position)

Decompose the string into a list (let's say the string is str)

list = str.split(' ') #This decomposes str with whitespace and creates a list with each as an element of the list.

A list with n elements and 0 elements

list = [0] * n

Reverse the list

list.reverse()

Concatenate lists that have strings as elements into strings

"".join(list) # ""If you put a specific symbol inside, that character is put in between and connected

Get a list in which each element of a list with int as an element is converted to a string

map(str, list)

Delete and cut list elements

del(list[index]) #Delete element
list.pop(index) #This is a cut, so
list1.append(list2.pop()) #You can add the last element of list2 to the end of list1
#By the way, pop()If no argument is specified for, the last element is targeted.

List with numbers from 0 to 9 as elements (list comprehension)

list = [i for i in range(10)]
list = [i for i in range(10) if i % 2 == 0] #In addition, if statements can be included

Checks for elements in the list and returns a dictionary where the key is the element in the list and the value is the number of times the key appears.

import collections
list = ['a', 'b', 'c', 'b', 'd', 'a']
counter = collections.Counter(list) # -> {'a':2, 'b':2, 'c':1, 'd':1}

sort

Sort in ascending order

sorted(list) #Sort the elements in the list in ascending order
sorted(dict.keys()) #Sort the dictionary in ascending key order
sorted(dict.items(), key=lambda x:x[1]) #Sort the dictionary in ascending order of value

Sort in descending order

sorted(list, reverse=True) #Just assign True to the reverse argument

Variable scope

Global variables

count = 0
def add_count():
    global count    #Access variables defined outside the function and
                    #Add global to apply the change outside the function
    count += 1