A summary of the language basics of Python (ii) loop and string manipulation

I. Loops and Branches

1. Conditional branching statements

If condition:

code block

Else

code block

2. While of the Loop statement

Think 1: Find the value of 1+2+3+....+10

　　

sum =1 while num < 101    :+ = num    + = 1print(sum)

For loop

For statement:

code block

Second, string manipulation

1. Concatenation of strings

Use the plus sign to link

#字符串的链接, through "+'welcome' toGuangzhou'  + s2)

Use "," to link

S1 = ' Hello ' s2 = ' world ' Print (S1, S2) #使用 "," when linking, the position of "," will produce a space

Use% formatting links

' Hello '  'World'print ("%s%s"% (S1, S2))

Linking using the Join function

S1 = ['hello'' World']print ("" . Join (S1))

Note: the ". join* () function only needs to pass one parameter inside.

2. Repeating the output string

' Good '  3)

3. Get the characters in a string

#通过索引的方式实现 # Index: The number of characters in a string is numbered from 0, which also becomes the value range of the Subscript # index: [0, str.length-1' Good ' print (str3[0]) #索引值还可以从-1 start, 1 for theCountdown first character print (str3[-1])

4. Intercepting strings

#通过索引的方式实现 # Index: The number of characters in a string is numbered from 0, which also becomes the value range of the Subscript # index: [0, str.length-1'  Good'print (str3[0]) #索引值还可以从-1 start, 1 for the lastcharacter print (str3[- 1])

5. Determine if the specified character is included

" You is a good boy " Print ("good" in str4) #若包含有则返回True否则为False

6. Formatted output

#通过% to change the meaning of the following letters orsymbols, %% of " Lili "  45.5 print ("My name is%s, I am%d year old and my weight is%.2f kg
     c13>"%(name, age, Weight)) #注意:%.nf indicates the precision to n digits after the decimal point, rounding

Three, about the common function of string

1.eval (str)

Function: evaluates the string str as a valid expression and returns the result of the calculation. You can convert List,tuple,dict,set and string to each other.

>>>num1 = eval ('123')>>>Print (NUM1)123 >>>num2 = eval ("[1, 2, 3]")>>>Print (num2) [1  23]>>> num3 = eval ("12-3") >>> Print (num3)9

2.len (str)

Function: Returns the length of the current string (number of characters)

>>> Len ("you aregood")

3.str.lower ()

Function: Returns a string that turns uppercase letters in a string into lowercase letters

" Hello World ">>> print (str.lower ()) Hello World

4.str.upper ()

Function: Returns a string that converts a lowercase letter in a string to uppercase

" Hello World ">>> print (Str.upper ()) HELLO World

5.str.swapcase ()

Function: Returns a string that turns uppercase letters in a string into lowercase letters and lowercase letters to uppercase (string case inversion)

" Hello World ">>> print (Str.swapcase ()) HELLO World

6.str.capitalize ()

Function: Returns a first-letter uppercase, other lowercase string

" Hello World ">>> print (Str.capitalize ()) Hello World

7.str.title ()

Function: Returns a string with the first letter of each word capitalized

" Hello World ">>> print (Str.title ()) Hello World

8.str.center (Width[,fillchar])

Function: Returns a centered string of the specified width, fillchar as a fill character

" Hello World ">>> print (Str.center ("*"))****************** *hello world********************

9.str.ljust (Width[,fillchar])

Function: Returns a left-aligned string of the specified width, fillchar as a fill character. Use space padding by default

" Hello World ">>> print (str.ljust ("*")) HelloWorld ********* ******************************

　　

10.str.rjust (Width[,fillchar])

Function: Returns a left-aligned string of the specified width, fillchar as a fill character. Use space padding by default

" Hello World ">>> print (str.rjust ("*"))******************* Hello World

11.str.zfill (width)

Function: Returns a length of width string, the original string right-aligned, the front complement 0

" Hello World ">>> print (Str.zfill) 000000000000000000000000000000000000000Hello World 

12.str.count (str[, Strat][,end])

Function: Returns the number of occurrences of STR in a string, optionally specifying a range that, if not specified, is case-sensitive by default.

" Hello World ">>> print (Str.count ("hello"0))0 

13.str.find (Str1[,start],[,end])

Function: From left to right to detect whether the STR1 string contains a string, you can specify a range, by default from beginning to end.

Return is the first occurrence of the subscript, if not queried, then return-1

" Hello World " " Llo " 0 Ten ))2

14.str.rfind (Str1[,start][,end])

Function: Similar to Str.find (), but from the right to start looking

" Hello World " " Llo " 0 Ten ))2

15.str.index (str1[strat=0],[end = Len (str)])

function is similar to find (), unlike find (), if STR1 does not exist, it will report an exception

" Hello World " " Hello " 0 Ten )) valueerror:substring not found

16.str.lstrip ()

Function: Truncate the string specified on the left side of the strings, by default removing whitespace characters (including ' \ n ', ' \ R ', ' \ t ', ')

' * * * * very good '>>> print (Str.lstrip ())>>> print (Str.lstrip ())* * * * * * * are very Good>>> print (Str.lstrip ("*")) Very good

17,str.rstrip ()

Function: Truncate the string specified to the right of the strings, the default is to remove the white space character (including ' \ n ', ' \ R ', ' \ t ', ')

' * * * * good**** '>>> print (Str.rstrip ()* * * * * * good****>>> print (Str.rstrip (" * " )* * * * are good

18.str.strip ()

Function: Truncate the strings specified on both sides of the string, then the default is to remove the white space character (including ' \ n ', ' \ R ', ' \ t ', ')

" Hello World">>> str1.strip ()'Hello World        '

19.string.split (str = ", Num=string.count (str))

Function: Slice string with the str divider, and if NUM has a specified value, only the NUM substring is split

The str--delimiter, which defaults to all empty characters, including spaces, line breaks (\ n), tab characters (\ t), and so on. num--split Times

>>> str1 ="Hello you is good">>>str1.split () ['Hello',' You',' is','Good']>>> Str1.split (" ",2)['Hello',' You','is good']

Practice:

1. Calculate thenumber of all the numbers that can be divisible by 3 or 17 within 1~ 100 and 2. Calculates the numberof daffodils in 100-999.  3. CalculateThe number of numbers that can be divisible by 7, but not even, within 200~ 500.  4"one-time   Input"--"one-time investment"  --The lottery--"winning/not winning-"user input Continue " Automatically exits the game "5" when the balance is 0. Hundred money to buy hundred chickens, existing 100 text money, Rooster 5 text Money A, hen 3 text money A, chicken a text money 3 only, Request: Rooster, hen, chicken to have, buy 100 chickens, put 100 of money spent, buy chicken is an integer. How many cocks, how many hens how many chickens?

　　

　　

A summary of the language basics of Python (ii) loop and string manipulation