Day Notes - string operation (escape conventional method, the output format), data type conversion, and a list of two methods of operation

First, the escape string 
    \ n newline ------> newline 
    \ t vertical tab ------> Click ab key == "" (four spaces) 
    \\ backslash the symbol ------> \ 
    R & lt ------> before the string plus r, for example, possible to prevent the string "\ r \ n \ b" 
expand: 
\ 'single quote \ "A \' -------> 'A' 
\ "double quote \" A \ "-------->" A " 
\ A bell python \ ajava --------> python? Java ' 
\ B backspace Python \ bphp --------> pythonphp 
\ 0 spaces Python \ 0php ---------> Python PHP 
\ R & lt carriage ------> enter key 
Second, the conventional method of the string 
    1, join methods: string concatenation 
        example: 
        input: 
           . D = '*' the Join ( 'CONT') 
           Print (D) 
        Output: O * * C * T n- 

    2, Find method: Find String element specified 
       default is traversed to find a string may be specified search 
    3, count method: Find string specified element The number of 
        default statistics all, you can also specify Find
    4, replace methods: replacement string in fragments 
        replace (a, b, c) 
        parameters a: string to be replaced string fragment 
        Parameter B: fragments replace the string 
        parameter c: the number of the replacement string segments the default is the replacement of all, this parameter can be used to control the number of times replacing 
    5, split method: split the string 
        split (a, b) 
        parameters of a: a string the string segment division point as 
        the parameter B: the default parameters as a whole is divided division point, can use this parameter to control the number of segmentation of 
        the final output is a list 
    . 6, upper method: all converted into lowercase letters capitalized string 
    7, lower method: the upper opposite 
three, format formatted output: by the string as a template, the parameters passed to format, using {} placeholder 
    1, the primary usage 
        name = input ( "enter your name:") 
        info = "my name is: {}" format (name). 
        Print (info) 
    2, advanced usage: 
        2.1 by the underlying index value passed in {}, to control the data format of the position 
            s = "{0 name }, {2} age, gender: ". Format (" {1 } red "," F ",
            Print (S) 
        2.2 by means of parameters passed in the {} are used to control the position of the data format of 
            s = "Name {name}, Age {} Age, Gender: {sex}". format ( name = " Small red ", sex =" female ", Age =" 18 is ") 
            Print (S) 
        when the advantage that, can be adjusted in the placement data format 
        2.3 by" {: a}. "format (b) to b accounting position designated length (a), (a> b, a space to fill the seats, the default fill the seats left) 
            left 
            name = "Sheng Yuan" 
            S = "my name is {: 5}, 25-year-old" .format (name) 
            Print (S) 
            right 
            name = "Sheng Yuan" 
            S = "my name is {:> 5}, 25 years old this year," .format (name) 
            Print (S) 
            middle 
            name = "Sheng Yuan" 
            S = "my name is {: 5} ^, 25 years old this year."the format (name) 
            Print (S) 
        2.4 format floating point control (number of decimal places)
            Expression: s = "numbers: {:. af}" format ( b) a:. Decimal digits of the display, b: floating point format need 
            s = "numbers: {:. 2f}" format ( 2.222222). 
            print (s) 
        percentage value 2.5 formatting 
            expression: s = "numbers: {:. a%}". format (b) a: number of digits after the decimal point show the percentage, the default is 2, b: requires formatting the percentage of 
            s = "numbers: 0 {%} :." the format (.555555). 
            Print (S) 
    . 3, the conventional output format 
        # conventional methods formatted output 
        # to use placeholder% 
        #% F only placeholder numeric type, the display is in the form of decimal 
        #% d occupying only numeric type, the display is an integer of 
        #% s universal placeholder (strings, floating point, integer) 
        # SS = "Python :% s, Age:% I "% (" 6666 ", 29) 
        # SS =" Python:% s, Age:% D "% (" 6666 ", 29) 
        # Print (SS) 
        # Print (" name: % s, age:% d "% ( 'Zhonguo', 2019)) 
    . 4, the extended expression F (preferably one, currently less popular)
        # String Defines the time with the addition of F / F. 
        Name = "China" 
        Sex = "MALE" 
        Age = 18 is 
        S2 = F. "Name {name}, Age {age}, Sex Sex} {:" 
        Print (S2) 
four , converting data types 
    # integer, float switch string, using STR 
    # string, floating-point to integer, using the int 
    # integer, floating-point string transfer, using a float 
    # integer, string, floating point, use BOOL 
    # NOTE: string to turn int / time folat, the contents of the string must be a number, (string not exist) 
V. list 
    Definition: use [] to represent the list, the list element can be any type of 
    elements in the list use spaced 
    list elements operating 
    index value index 
    slice 
    len (strings, tuples, lists, dictionaries, set) Gets a list (number of elements) in the (length) 

    List1 = [ 'a',. 1, { ' name ':' Yuanxiao Song '}, True, 1.1] 
    # subscript values 
    S = List1 [2] 
    Print (S) 
    # slices, by the value of the element value of the index
    List1 = S1 [-1: -3: -1] 
    Print (S1) 
    # len (), built-in function 
    S2 = len (List1) 
    Print (S2) 
six, the operation method in the list of elements 
    increasing element method: 
    the append 
    INSERT 
    Extend 
    = Li [. 1, 2,. 3] 
    # the append method, is added to the end of the list elements 
    # li.append (999) 
    # Print (Li) 
    # iNSERT: Specifies the position of the insertion element 
    # iNSERT (index, Object) 
    # first parameter: 
    the second parameter #: 
    # li.insert (. 1, 25) 
    # Print (Li) 
    # Extend add multiple elements in a list 
    # li.extend ([11,222,2333]) 
    # Print (Li) 

    to remove elements 
    remove : delete the specified elements of 
    pop: according to the index to delete the corresponding elements 
    clear: clear the list 
    # remove Note: remove elements that do not exist will complain
    Li.remove # (2) 
    # Print (li) 
    # POP not pass parameters, default remove the last, to remove the target elements specified by the transfer parameter 
    # li.pop () 
    # Print (li) 
    # the Clear 
    # li.clear ( ) 
    # Print (li)