Python learning Notes (String)

a variables

1 Creating a variable: d=4 means assigning an integer object ' 4 ' to the variable D

Remember: All data is an object

Remember: All variables are a reference to a data object

Analysis: The reference count inside Python. Sys.getrefcount

2 Variable Naming conventions:

(1) Use only letters and underscores

(2) cannot use keywords such as if and so on

(3) Case sensitive

3 Assignment:

Remembering Polymorphic Properties

Multiple assignments

Delete: Del

An equal sign = is an assignment, and two equals = = is a comparison

Note: The three built-in must be cooked. Type,help,dir

4 Common basic data types:

(1) Int integral type

(2) Boolean Boolean value

(3) String strings

(4) List

(5) Tuple tuples

(6) Dict dictionary

5 variable and non-volatile data types

(1) Immutable type: int, string, tuple (by ID () unique identifier)

(2) Variable type: list, dict

two string : Help (str)

1 accessing strings, sequences

A= ' Wujiadong '

Print (A[0])

Print (Len (a))

Print (A[8])

Print (a[:])

2 Replacement string

B=a.replace (' Wujiadong ', ' Jiangrui ') #前面是老字符串, followed by a new string, note to enclose

Print (b)

3 string concatenation

Method One: "Pass the + number"

A= ' Wujiadong '

B= ' Jiangrui

C= ' a ' + ' B ' # + number stitching

Print (A+B)

Method Two: "Through placeholder%"

A= ' My name is Wujiadong. '

Print (a)

B= ' My name is%s wujiadong '% ' Xiaowu ' #

Print (b) Result: My name is Xiaowu Wujiadong

%s-placeholders for strings

%d-placeholders for numbers

Method Three: The best way to ". Join ()"

A= ' Wu '

b= ' Jia '

C= ' Dong '

D1= '. Join ([a,b,c])

D2= ' * '. Join ([a,b,c])

Print (D1) Result: Wujiadong

Print (D2) Result: Wu*jia*dong

4 Read and write text

W-write R-read A-append

A=open (' A.txt ', ' W ') #创建打开文件

A.write (' Hi.\nsecond hi. ') #写内容只能写字符串

A.close () #关闭文件

A=open (' A.txt ', ' R ') #这里写完后可以help (d) See which methods are read

Print (list (a)) Result: [' hi.\n ', ' second hi. '] The #用list () conversion function returns the actual contents of the file (in the form of a list)

#这里如果直接打印a会报错. A is a file object

Print (A.read (100)) Result: The result can be directly output, 100 can not write. If re-read, need A.seek (0)

#两次输出

Print (A.readline ()) Result: output Hi and blank line

Print (A.readline ()) Result: Output second hi

>>> a=open (' 1.txt ', ' R ')

>>> a=open (' 1.txt ', ' W ')

>>> a.write (' wowowo\naiaiaiai\nyouyouyou ')

25

>>> A.close ()

>>> a=open (' 1.txt ', ' R ')

>>> Import Linecache

Via Module Linecache

Print (Linecache.getline (' 1.txt ', 1))

Or

>>> lines=linecache.getlines (' 1.txt ')

>>> Print (lines)

5 Modifying strings

A= ' This is Jiadong '

A=a.replace (' This ', ' that ') #替换

Print (a) result: that's Jiadong

6 string formatting

(1) through the format () function:

Print (' {0} love {1} {2} '. Format (' I ', ' Jia ', ' dong ') result I love Jia Dong

Print (' {} {} '. Format (' Jia ', ' dong ') result Jiadong

Print (' {1}{0}{1} '. Format (' Jia ', ' dong ') result Dongjiadong

(2) by keyword:

Print (' {A} love {b} {c} '. Format (a= ' i ', b= ' Jia ', c= ' dong ')) result I love Jia Dong

Print (' {0} love {a} {b} '. Format (' Jia ', a= ' Wu ', b= ' dong ') result Jia Love Wu Dong #综合使用, positional parameters must be before the keyword parameter

(3) by subscript:

p=[' Jiadong ', 18]

Print (' {0},{0} '. Format (p)) results [' Jiadong ', 18],[' Jiadong ',] #两0之间可以有逗号, or no comma

Print (' {0[0]},{0[1]} '. Format (p)) Results jiadong,18

7 Format qualifier: (Syntax is {} with: #)

A Fill and align:

(1) Padding is used in conjunction with alignment

(2) ^, <, > is centered, left-aligned, right-aligned, followed by width

(3): The character after the number is filled, can only be one character, not specified by default with a space padding

Print (' {: >8} '. Format (' 189 ')) Results 189 #大于号右边靠

Print (' {: <8} '. Format (' 189 ')) Results 189 #小于号左边靠

Print (' {: 0<8} '. Format (' 189 ')) results 18900000 #用0填充

Print (' {: a>8} '. Format (' 189 ')) results aaaaa189 #用a填充

B precision and type F

Print (' {:. 2f} '. Format (321.33345)) Results 321.33 # where. 2 represents a precision of 2 length, and F indicates the folder type

C Other types

(1) mainly in the system, B, D, O, X are binary, decimal, octal, hexadecimal.

Print (' {: b} '. Format (17)) Result 10001

Print (' {:d} '. Format (17)) result 17

Print (' {: o} '. Format (17)) Result 21

Print (' {: x} '. Format (17)) Result 11

(2) The thousand separators that can be used to make the amount

Print (' {:,} '. Format (1234567890)) result 1,234,567,890

D string Formatting symbolic meaning

(1)%c formatted string machine ASCII code

Print ('%c '% 97) result A

Print ('%c%c%c '% (97,98,99)) results a B C

(2)%s formatted string

Print ('%s '% ' I love wujiadong ') result I love Wujiadong

(3)%d formatted integer

Print ('%d+%d=%d '% (4,5,4+5)) Results 4+5=9

(4)%o formatting unsigned octal numbers

Print ('%o '% 10) Results 12

(5)%x format unsigned hexadecimal number

Print ('%x '% 10) result A

(6)%x formatted unsigned hexadecimal number (uppercase)

Print ('%x '% 10) result A

Print ('%e '%27.123) results A0

(7)%f formatted fixed-point number, you can specify the precision after the decimal point

Print ('%f '%27.123) results 27.123000

(8)%e of fixed-point number by scientific method

Print ('%e '%27.123) results 2.712300e+01

(9)%e with%e

Print ('%E '%27.123) results 2.712300E+01

(%g) Depending on the size of the value, use%f or%e

Print ('%g '%27.123) results 27.123

(one)%g effect with%g

Print ('%G '%27.123) results 27.123

E string formatting operator auxiliary instruction

Python learning Notes (String)