Python Course design Notes (iii) integers, floating-point numbers, and strings

Integer type (range unlimited)

Decimal 1-1

Binary 0b1-0b1

Octal 0o1-0o1

Hex 0x1-0x1

Floating-point type (limited in scope but negligible)

　　an indeterminate mantissa is present in the operation:0.1+0.2!=0.3

Cause: Binary means that decimals can be infinitely close but not identical, generating indeterminate decimals during conversion

How to avoid: floating point key operation and comparison with round () function for auxiliary round (x, D) #对x进行四舍五入, D is to intercept the number of decimal digits

Scientific notation for floating-point numbers <a>e<b> # a*10^b

Numeric Operation operators

10/3 = 3.3333

10//3 = 3

X**y #x ^y

mixed operations between types: Generate results widest type complex number > floating point number > Integer 123

　　

Numeric arithmetic functions

Absolute ABS ()

Shangyu divmod (x, y) output (quotient, remainder)

Power Surplus pow (x,y[, z]) output (x**y)%z for the last few of X**y

Rounding round (x [, d]) x reserved d decimal, default D is 0

Maximum minimum value max/min (x1,x2,x3,..)

cast int (decimal, string) discards decimals directly

Float (integer, String) is an integer plus a fractional part

String type

　　Representation method:

1) A pair of single quotes, a pair of double quotation marks, representing only a single line string

2) A pair of three single quotes, or three double quotation marks, representing multiple lines of string

　　the ordinal of a string ( two sequence numbers exist simultaneously in a string ): Forward increment inverse decrement (last-1, left- -2,-3,,,)

　　Index and slice of a string

Index "Hello" "0" or str "0"

slicing (slice)　　　　 (copyright:https://www.cnblogs.com/cedrelaliu/p/6004352.html)

A slice operation (slice) can get a substring (part of a string) from a string. Start offset start, end offset end, optional step step define a shard.

Format: [Start:end:step]

• • [:] Extracts the entire string from the beginning (default position 0) to the end (default position-1)
  • [Start:] Extract from start to end
  • [: end] Extract from the beginning to End-1
  • [Start:end] extracted from start to end-1
  • Start:end:step] Extract from start to end-1, each step character extracts one

Special: Reverses the string by reversing the string (reverse) by setting the step to a negative number: [::-1]

　　

　　Operators for string Operations:

X+y: Link Two strings

N*x or X*n: Copy n-Times string X

Whether x in S:x is a substring of s, returns TRUE or False

　String handling functions

Len (x): The length of the string x, and the length of a Chinese character and an English letter is 1

STR (x): string coercion type conversion, any type x converted to string = = = Opposite eval ()

Hex (x) and Oct (x): Converts x into octal and hexadecimal form

Chr (U): x is Unicode encoded and returns its corresponding characters

Ord (x): X is a character that returns the corresponding Unicode encoding

Note: Python uses Unicode encoding uniformly

Str.lower () Str.upper ()

Str.split ("")

Str.count ("a")

Str.replace (old,new)

Str.center (Width[,fillchar])

Str.strip ("=pn" _

Str.join ("1234") STR join to "1234"

　　

　　Formatting of the string output

　　　　slot : "< {} {} >". Format ("Ch1", "CH2")

　　　　Format control parameters in slots

　　　　　　

　　　　

Time Library:

Standard library for processing time

　Time Acquisition:

Time () #获取时间戳: A floating-point number, in seconds, starting from 1970

CTime () #获取一可读的字符串 Mon May 14 22:51:40 2018

Gmtime () #其他程序可利用的时间格式 time.struct_time (tm_year=2018, tm_mon=5, tm_mday=14, tm_hour=14, tm_min=52, tm_sec=25, tm_wday= 0, tm_yday=134, tm_isdst=0)

　　

　　Time formatting:

Show time in a reasonable way

Strftime (Tpl,ts) #tpl是输出格式模板 (String) str is gmtime ()

Controls in the TPL:

%y year,%m month,%b month name,%b month name abbreviation ...

　　Program Timings:

Measurement Time Perf_counter () #返回CPU级别的精确时间计数值, units in seconds, difference is meaningful

Sleep Time.sleep (time) #停滞t秒

Instance:

The creation of a text progress bar

Import Timeprint ("---execution start---") Scale=TenStart=Time.perf_counter () forIinchRange (scale+1): Du= Time.perf_counter ()-Start a='*'*I b="."* (scale-i) C= (i/scale) * -Print ("\r{:>3.0f}%[{}->{}]{:.2f}s". Format (C,A,B,DU), end=" ") Time.sleep (0.32)

Controlling the Print function

\ r cursor returns to the beginning of the current line

Print (< string >,end= "printing end character" >

Note that in idle in order to display the full information auto-mask \ r, the py file is run on the command line

　　

　　

Python Course Design notes (three) integers, floating-point numbers, and strings