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"))

DirectiveDescriptionExample%aWeekday, short versionWed%AWeekday, full versionWednesday%wWeekday as a number 0-6, 0 is Sunday3%dDay of month 01-3131%bMonth name, short versionDec%BMonth name, full versionDecember%mMonth as a number 01-1212%yYear, short version, without century18%YYear, full version2018%HHour 00-2317%IHour 00-1205%pAM/PMPM%MMinute 00-5941%SSecond 00-5908%fMicrosecond 000000-999999548513%zUTC offset+0100%ZTimezoneCST%jDay number of year 001-366365%UWeek number of year, Sunday as the first day of week, 00-5352%WWeek number of year, Monday as the first day of week, 00-5352%cLocal version of date and timeMon Dec 31 17:41:00 2018%CCentury20%xLocal version of date12/31/18%XLocal version of time17:41:00%%A % character%%GISO 8601 year2018%uISO 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

PythonJSONdictObjectlistArraytupleArraystrStringintNumberfloatNumberTruetrueFalsefalseNonenull

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

FunctionDescriptionfindallReturns a list containing all matchessearchReturns a Match object if there is a match anywhere in the stringsplitReturns a list where the string has been split at each matchsubReplaces one or many matches with a string

元字符是具有特殊含义的字符

CharacterDescriptionExample[]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

CharacterDescriptionExample\AReturns a match if the specified characters are at the beginning of the string"\AThe"\bReturns 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"ain\b"\BReturns 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"ain\B"\dReturns a match where the string contains digits (numbers from 0-9)"\d"\DReturns a match where the string DOES NOT contain digits"\D"\sReturns a match where the string contains a white space character"\s"\SReturns a match where the string DOES NOT contain a white space character"\S"\wReturns a match where the string contains any word characters (characters from a to Z, digits from 0-9, and the underscore _ character)"\w"\WReturns a match where the string DOES NOT contain any word characters"\W"\ZReturns a match if the specified characters are at the end of the string"Spain\Z"

集合是一对方括号[]内的一组字符，具有特殊含义

SetDescription[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 n1Returns 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 90-5Returns 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, +, *, ., `, (), $,{} has no special meaning, so [+] means: return a match for any +` character in the string

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"\bS\w+", 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"\bS\w+", 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"\bS\w+", txt)
print(x.group()) # Spain

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arn ↩