Number, date, time

1, we want to take a floating point number to the fixed decimal place

Use the built-in round (value,ndigits) to:

1 >>> round (1.23,1)2 1.23 >>> round (1.27,1)4 1.35 >>> round ( -1.27,1)6 -1.37 >>> round (1.1231237,3 )8 1.1239

Ndigits can be negative, in which case it will be rounded to 10 bits, hundreds of thousands, etc., such as:

1 >>> round (1.1231237,3)  2 1.123 3 >>> a = 1231231 4 >& Gt;> round (a,-1)  5 1231230 6 >>> round (a,-2)  7 1231200 8< /c10> >>> Round (a,-3)  9 1231000

The output of the value can not be confused with the formatted output, if only to let the value of a fixed number of digits output, generally do not round ():

1>>> x = 1.234562>>> Format (x,'0.2f')3 '1.23'4>>> Format (x,'0.3f')5 '1.235'6>>>'value is {: 0.3f}'. Format (x)7 'value is 1.235'

To perform a precise decimal operation, let's take a look at the following small example:

1 >>> a = 4.22 >>> B = 2.13 >>> A + b4 6.300 0000000000015 >>> (A + b) = = 6.36False7

Actually false, these errors are essentially a feature of the underlying CPU's floating-point unit and the IEEE754 floating-point arithmetic standard, so how to avoid such errors and get higher accuracy (sacrifice a bit of performance), you can use the decimal module

1>>> fromDecimalImportDecimal2>>> a = Decimal (4.2)3>>> B = Decimal (2.1)4>>> A +b5Decimal ('6.300000000000000266453525910')6>>>Print(A +b)76.3000000000000002664535259108>>> A = Decimal ('4.2')9>>> B = Decimal ('2.1')Ten>>> A +b OneDecimal ('6.3') A>>>Print(A +b) -6.3 ->>> (A + b) = = 6.3 the False ->>> (A + b) = = Decimal ('6.3') - True ->>>

Note quotation marks

Time Conversion

#_ *_coding:utf-8_*_
Import time
Import datetime

Print (Time.clock ()) #返回处理器时间, 3.3 started obsolete
Print (Time.process_time ()) #返回处理器时间, 3.3 started obsolete
Print (Time.time ()) #返回当前系统时间戳
Print (Time.ctime ()) #输出Tue Jan 26 18:23:48 2016, current system time
Print (Time.ctime (Time.time () -86640)) #将时间戳转为字符串格式
Print (Time.gmtime (Time.time () -86640)) #将时间戳转换成struct_time格式
Print (Time.localtime (Time.time () -86640)) #将时间戳转换成struct_time格式, but the local time returned
Print (Time.mktime (Time.localtime ())) #与time. LocalTime () function instead, turn struct_time format back into timestamp format
#time. Sleep (4) #sleep
Print (Time.strftime ("%y-%m-%d%h:%m:%s", Time.gmtime ())) #将struct_time格式转成指定的字符串格式
Print (Time.strptime ("2016-01-28", "%y-%m-%d")) #将字符串格式转换成struct_time格式

#datetime Module

Print (Datetime.date.today ()) #输出格式 2016-01-26
Print (Datetime.date.fromtimestamp (Time.time () -864400)) #2016-01-16 turn the timestamp into a date format
Current_time = Datetime.datetime.now () #
Print (current_time) #输出2016-01-26 19:04:30.335935
Print (Current_time.timetuple ()) #返回struct_time格式

#datetime. replace ([year[, month[, day[, hour[, minute[, second[, microsecond[, Tzinfo] []] []])
Print (Current_time.replace (2014,9,12)) #输出2014-09-12 19:06:24.074900, returns the current time, but the specified value is replaced

Str_to_date = Datetime.datetime.strptime ("21/11/06 16:30", "%d/%m/%y%h:%m") #将字符串转换成日期格式
New_date = Datetime.datetime.now () + Datetime.timedelta (days=10) #比现在加10天
New_date = Datetime.datetime.now () + Datetime.timedelta (days=-10) #比现在减10天
New_date = Datetime.datetime.now () + Datetime.timedelta (hours=-10) #比现在减10小时
New_date = Datetime.datetime.now () + Datetime.timedelta (seconds=120) #比现在 +120s
Print (new_date)

Number, date, time