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"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
您的关注，是我的无限动力!
公众号 @生活处处有BUG
