Python入门系列(八)日期时间、数学、json

日期时间

Python中的日期本身不是数据类型,但我们可以导入一个名为datetime的模块,将日期作为日期对象使用。

import datetime

x = datetime.datetime.now()
print(x)

日期输出

import datetime

x = datetime.datetime.now()

print(x.year)
print(x.strftime("%A"))

创建日期对象

import datetime

x = datetime.datetime(2020, 5, 17)

print(x)

strftime()方法

import datetime

x = datetime.datetime(2018, 6, 1)

print(x.strftime("%B"))
Directive Description Example
%a Weekday, short version Wed
%A Weekday, full version Wednesday
%w Weekday as a number 0-6, 0 is Sunday 3
%d Day of month 01-31 31
%b Month name, short version Dec
%B Month name, full version December
%m Month as a number 01-12 12
%y Year, short version, without century 18
%Y Year, full version 2018
%H Hour 00-23 17
%I Hour 00-12 05
%p AM/PM PM
%M Minute 00-59 41
%S Second 00-59 08
%f Microsecond 000000-999999 548513
%z UTC offset +0100
%Z Timezone CST
%j Day number of year 001-366 365
%U Week number of year, Sunday as the first day of week, 00-53 52
%W Week number of year, Monday as the first day of week, 00-53 52
%c Local version of date and time Mon Dec 31 17:41:00 2018
%C Century 20
%x Local version of date 12/31/18
%X Local version of time 17:41:00
%% A % character %
%G ISO 8601 year 2018
%u ISO 8601 weekday (1-7) 1

数学

min()和max()函数可用于查找可迭代中的最低或最高值

x = min(5, 10, 25)
y = max(5, 10, 25)

print(x)
print(y)

函数的作用是:返回指定数字的绝对(正)值

x = abs(-7.25)

print(x)

pow(x,y)函数将x的值返回到y(xy)的幂。

# Return the value of 4 to the power of 3 (same as 4 * 4 * 4)
x = pow(4, 3)

print(x)

数学模块

import math

x = math.sqrt(64)

print(x)

ceil()方法将一个数字向上舍入到其最接近的整数,然后进行数学运算。floor()方法将数字向下舍入到最接近的整数,并返回结果

import math

x = math.ceil(1.4)
y = math.floor(1.4)

print(x) # returns 2
print(y) # returns 1

pi常量,返回pi的值(3.14…)

import math

x = math.pi

print(x)

JSON

从JSON转换为Python

import json

# some JSON:
x =  '{ "name":"John", "age":30, "city":"New York"}'

# parse x:
y = json.loads(x)

# the result is a Python dictionary:
print(y["age"])

从Python转换为JSON

import json

# a Python object (dict):
x = {
  "name": "John",
  "age": 30,
  "city": "New York"
}

# convert into JSON:
y = json.dumps(x)

# the result is a JSON string:
print(y)

您可以将以下类型的Python对象转换为JSON字符串.

当您从Python转换为JSON时,Python对象将转换成JSON(JavaScript)等价物

Python JSON
dict Object
list Array
tuple Array
str String
int Number
float Number
True true
False false
None null

格式化结果

使用缩进参数定义缩进的数量

json.dumps(x, indent=4)

您还可以定义分隔符,默认值为(“,”,“:”,这意味着使用逗号和空格分隔每个对象,使用冒号和空格分隔键和值

json.dumps(x, indent=4, separators=(". ", " = "))

json_dumps()方法有参数来对resu中的键进行排序

json.dumps(x, indent=4, sort_keys=True)

正则表达式

Python有一个名为re的内置包,可用于处理正则表达式。

import re

正则表达式函数

Function Description
findall Returns a list containing all matches
search Returns a Match object if there is a match anywhere in the string
split Returns a list where the string has been split at each match
sub Replaces one or many matches with a string

元字符是具有特殊含义的字符

Character Description Example
[] A set of characters "[a-m]"
Signals a special sequence (can also be used to escape special characters) "d"
. Any character (except newline character) "he..o"
^ Starts with "^hello"
$ Ends with "planet$"
* Zero or more occurrences "he.*o"
+ One or more occurrences "he.+o"
? Zero or one occurrences "he.?o"
{} Exactly the specified number of occurrences "he.{2}o"
| Either or "falls|stays"
() Capture and group

特殊序列

Character Description Example
A Returns a match if the specified characters are at the beginning of the string "AThe"
b Returns a match where the specified characters are at the beginning or at the end of a word (the "r" in the beginning is making sure that the string is being treated as a "raw string") r"bain" r"ainb"
B Returns a match where the specified characters are present, but NOT at the beginning (or at the end) of a word (the "r" in the beginning is making sure that the string is being treated as a "raw string") r"Bain" r"ainB"
d Returns a match where the string contains digits (numbers from 0-9) "d"
D Returns a match where the string DOES NOT contain digits "D"
s Returns a match where the string contains a white space character "s"
S Returns a match where the string DOES NOT contain a white space character "S"
w Returns a match where the string contains any word characters (characters from a to Z, digits from 0-9, and the underscore _ character) "w"
W Returns a match where the string DOES NOT contain any word characters "W"
Z Returns a match if the specified characters are at the end of the string "SpainZ"

集合是一对方括号[]内的一组字符,具有特殊含义

Set Description
[arn] Returns a match where one of the specified characters (a, r, or n) is present
[a-n] Returns a match for any lower case character, alphabetically between a and n
[^arn] Returns a match for any character EXCEPT a, r, and n
[0123] Returns a match where any of the specified digits (0, 1, 2, or 3) are present
[0-9] Returns a match for any digit between 0 and 9
[0-5][0-9] Returns a match for any two-digit numbers from 00 and 59
[a-zA-Z] Returns a match for any character alphabetically between a and z, lower case OR upper case
[+] In sets, +, *, ., `

findall()函数的作用是:返回一个包含所有匹配项的列表。

import re

txt = "The rain in Spain"
x = re.findall("ai", txt)
print(x)

该列表按找到的顺序包含匹配项。
如果未找到匹配项,则返回空列表

import re

txt = "The rain in Spain"
x = re.findall("Portugal", txt)
print(x)

search()函数的作用是:在字符串中搜索匹配项,如果存在匹配项,则返回匹配对象。

import re

txt = "The rain in Spain"
x = re.search("s", txt)

print("The first white-space character is located in position:", x.start())

split()函数的作用是:返回一个列表,其中字符串在每次匹配时被拆分

import re

txt = "The rain in Spain"
x = re.split("s", txt)
print(x)

可以通过指定maxsplit参数来控制出现次数

import re

txt = "The rain in Spain"
x = re.split("s", txt, 1)
print(x)

sub()函数的作用是:用您选择的文本替换匹配项

import re

txt = "The rain in Spain"
x = re.sub("s", "9", txt)
print(x) # The9rain9in9Spain

您可以通过指定count参数来控制替换的数量

import re

txt = "The rain in Spain"
x = re.sub("s", "9", txt, 2)
print(x)

匹配对象是包含有关搜索和结果的信息的对象。

注意:如果没有匹配,将返回值None,而不是match对象。

.span()返回包含匹配的开始位置和结束位置的元组。

import re

txt = "The rain in Spain"
x = re.search(r"bSw+", txt)
print(x.span()) # (12, 17)

.string 返回传递到函数中的字符串

import re

txt = "The rain in Spain"
x = re.search(r"bSw+", txt)
print(x.string) # The rain in Spain

.group() 返回字符串中存在匹配项的部分

import re

txt = "The rain in Spain"
x = re.search(r"bSw+", txt)
print(x.group()) # Spain

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