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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 Returns a list containing all matches Returns a if there is a match anywhere in the string Returns a list where the string has been split at each match 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"ain\b" \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"ain\B" \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 "Spain\Z"

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"\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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