Cloud Classroom-python Learning notes (5)

• String definitions:
  • A string is a sequence of characters
  • Surround with paired single or double quotes
    • One_quote_str = ' Hello world! '
    • Two_quote_str = "Hello world!"

  • ? or three quotation marks ("" "or")
    Preserves all formatting information in a string

    • "This is
    • A test
    • Today ' "
• Basic string Operations
  • Length (len () function)

    1 ' python ' 2 print len (first_name)
    Output: 6

  • Stitching (+)

    1 ' python ' 2 ' Testing ' 3 Print Name
    Output: pythontesting

  • Repeat (*)

    1 ' python ' 2 Print name * 3

• Member operator (in)
  • Determines whether a string is a substring of another string, returns a value of TRUE or False

    1Name ='python'2 Print 'x' inchname//false3 Print ' on' inchname//true4 Print ' on' inchName//false, case sensitive

• For statement, each character in the enumeration string

  ' python '  for inch Name:     Print CPython

• example, count the number of vowels in a string

  1 defVowles_count (s):2Count =03      forCinchS:4         ifCinch 'Aeiouaeiou':5Count + = 16     returnCount7 8 PrintVowles_count ('Hello world!')

• String index (indexed)
  • Each character in the string is indexed with an index value (subscript)
  • Index starts at 0 (forward) or-1 (backwards)

    1str ='Hello World'2 3 PrintStr[2]4 PrintStr[-3]5 PrintStr[15]6 7 L8 R9 Traceback (most recent):TenFile"<stdin>", Line 1,inch<module> OneFile"C:\Python27\lib\site-packages\spyderlib\widgets\externalshell\sitecustomize.py", Line 540,inchRunfile A execfile (filename, namespace) -File"c:/users/weidan/desktop/untitled0.py", Line 12,inch<module> -     PrintStr[15] theIndexerror:string index out of range

• Slicing (slicing)
  • Select a subsequence of a string
  • Grammar [Start:finish]
    • Start: The position at which the sub-sequence begins
    • Finish: The index value of the next character in the ending position of the subsequence
    • if start or finish is not provided, the default start is the first character, and finish is the last character

        str =  '  

• Count parameters
  • Receive 3 parameters
    • [Start:finish:countBy]
    • The default countby is 1
  • Get inverse string

    1 ' Hello World ' 2 3 print str[2:6:2]4print str[::-1]//Get inverse string 5Print str[:6:2]67lo8dlrow Olleh9 Hlo

• The string cannot be changed.
  • Once generated, the content cannot be changed

    1str ='Hello World'2STR[1] ='a'3 PrintStr4 5 Traceback (most recent):6File"<stdin>", Line 1,inch<module>7File"C:\Python27\lib\site-packages\spyderlib\widgets\externalshell\sitecustomize.py", Line 540,inchRunfile8 execfile (filename, namespace)9File"c:/users/***/desktop/untitled0.py", Line 9,inch<module>TenSTR[1] ='a' OneTypeError:'Str'Object does notSupport Item Assignment A>>>

  • Generate a new string by slicing, etc.

    1 ' Hello World ' 2 ' a ' + str[2:]3print  str45 Hallo World  

Cloud Classroom-python Learning notes (5)