Python learning notes, python

Python learning notes, python

 

Display type

Python 3.6.1 (v3.6.1:69c0db5, Mar 21 2017, 17:54:52) [MSC v.1900 32 bit (Intel)] on win32Type "help", "copyright", "credits" or "license" for more information.>>> import types>>> type([])<class 'list'>>>> type(1)<class 'int'>

In REPL, if you want to display the type in the source code file, you must add print

import typesprint(type([]))a = 123;print(type(a))

 

Common Data Structures

List

The list is variable-length and can dynamically add elements. The element types are not required to be uniform, ordered, and repeatable.

Create an empty list in two ways

alist = []blist = list()

Directly create a list with elements

alist = ['one', 'two', 3, True];

 

Append an element to the end

alist.append('four') # api list.append(obj)

 

Add an element to a specified index

alist.insert(1, 'one point five') # api list.insert(index, obj)

Queries the elements of an index.

element1 = alist[0]element2 = alist[2]print(element1)print(element2)

 

Modify the element of an index

alist[3] = 'three'

Delete an element at an index location.

Alist = [1, 2, 3, 4] a = alist. pop (1) # Delete api, where the parameter is to be deleted, print (a) #2 print (alist) # [1, 3, 4] alist. pop () # delete the end print (alist) When no parameter is given # [1, 3]

 

Delete An element. If you do not know the index location

Alist = [1, 2, 2, 3] alist. remove (2) # delete an api. A parameter is the element to be deleted. If the element value is repeated, only the top element is deleted. No returned value print (alist) # [1, 2, 3]

Get list Length

size = len(alist)
print(size)

Traverse list

For v in alist: print (v) # v is the element value.

Retrieve indexes during Traversal

For idx, val in enumerate (alist): print (idx, val) # idx is the index and val is the element value

 

Reference: http://stackoverflow.com/questions/522563/accessing-the-index-in-python-for-loops

 

There are several elements for getting a value.

list = [1, 2 , 2, 4, 'a', 'a','b']print(list.count(2)) #2print(list.count('a')) #2

Obtain the maximum element

llist = [1, 2 , 3, 4, True]max = max(list) # apiprint(max) # 4

Be careful when using this api for mixed lists. For example, an error occurs when mixing int and str.

List = [1, 2, 3, 4, 'a'] max = max (list) print (max) run error Traceback (most recent call last): File "c: \ Users \ myname \ Documents \ pythonporjects \ test. py ", line 5, in <module> max = max (list) TypeError: '>' not ororted between instances of 'str' and 'int'

 

 

Tuple

Once the elements of the tuples are determined to be unchangeable, they can only be queried, And the tuples themselves cannot add or delete elements. Element types are not required to be uniform, ordered, and repeatable

Create an empty tuple in either of the following ways:

atuple = ()btuple = tuple()

Null tuple is of little use. Therefore, tuple elements are initialized when a tuple is created.

atuple = (1, 2 , 2, 4, 'a', 'b')print(atuple)

Tuple with only one element should be like this

atuple = (1, )print(atuple)

Query Element

atuple = (1, 2 , 2, 4, 'a', 'b')print(atuple[0])print(atuple[1])

If you try to modify the element value, an error is returned.

atuple[0] = 0Traceback (most recent call last):  File "c:\Users\myname\Documents\pythonporjects\test.py", line 8, in <module>    atuple[0] = 0TypeError: 'tuple' object does not support item assignment

 

Get tuple Length

t = (1, 2, 3)size = len(t) #apiprintln(size)

 

There are several elements for getting a value.

t = (1, 2 , 2, 4, 'a', 'a','b')print(t.count(2)) # 2print(t.count('a')) # 2

 

To obtain the largest element, refer to the list chapter.

Tuple unpacking

t = (1 ,2)a , b = tprint(a) # 1print(b) # 2

Reference http://stackoverflow.com/questions/10867882/tuple-unpacking-in-for-loops

 

Set

Set is similar to a set in mathematics. elements are unordered and cannot be duplicated.

There is only one way to create an empty set

aset = set()

Traverse the set. The index does not exist because it is unordered.

for el in aset:    print(el)

 

Traverse a set with a growth Length

 

Http://stackoverflow.com/questions/28584470/iterating-over-a-growing-set-in-python

Create an empty dictionary in either of the following ways:

adict = {}bdict = dict()

 

Traverse dictionary

Only Traverse key

for k in adict:    print(k) # k

Traverse key and value

for key, value in adict.items():    print(key, value)

Reference http://stackoverflow.com/questions/3294889/iterating-over-dictionaries-using-for-loops-in-python

 

Time and date Processing

 

#!/usr/bin/python# -*- coding:utf-8 -*-import timea = time.time()print("timestamp" , a)a = time.strftime("%Y-%m-%d %H:%M:%S", time.localtime()) print("now is", a)a = time.localtime()year = a.tm_yearprint("year is", year)

More references Python Date and Time | cainiao tutorial http://www.runoob.com/python/python-date-time.html

 

 

Reference

Http://www.runoob.com/python/python-tutorial.html

Http://www.liaoxuefeng.com/wiki/0014316089557264a6b348958f449949df42a6d3a2e542c000

Http://stackoverflow.com/questions/tagged/python

Https://www.dotnetperls.com/python