Chapter 14 strings
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Strings in Python are arrays of bytes representing Unicode characters. Individual characters in a string can be accessed using indexes and slices. Strings are immutable, so their elements cannot be changed once created. Various methods are available for string manipulation in Python. These include methods for accessing characters by index or slice, checking substrings, converting case, padding/stripping strings, and more. Character methods like ord() and chr() allow getting ASCII values and characters.
![Strings are immutable. This
means that elements of a string cannot be
changed once it has been assigned. We can
simply reassign different strings to the
same name.
>>> my_string = 'programiz'
>>> my_string[5] = 'a'
TypeError: 'str' object does not support
item assignment.
How to change or delete a string?](https://image.slidesharecdn.com/chapter14strings-190528090316/85/Chapter-14-strings-7-320.jpg)
![SLICING STRINGS EXAMPLES
For example:
>>>“Program”[3:5]
will result in:
‘gr ’
>>>“Program”[3:6]
will yield:
‘gra’
>>>p = “Program”
>>>p [:4]
‘Prog’
>>>p = “Program”
>>>p [4:]
‘ram’
>>>p = “Program”
>>>p [3:6]
‘gra’](https://image.slidesharecdn.com/chapter14strings-190528090316/85/Chapter-14-strings-21-320.jpg)
![More Functionality of String
>>> name1="computer"
>>> name2=name1[3:5]
>>>name2
pu String Slicing](https://image.slidesharecdn.com/chapter14strings-190528090316/85/Chapter-14-strings-26-320.jpg)
Chapter 14 strings
- 2. Unit 2: Computational Thinking and Programming XI Computer Science (083) Board : CBSE Courtesy CBSE
- 3. Unit II Computational Thinking and Programming (60 Theory periods 45 Practical Periods) DCSc & Engg, PGDCA,ADCA,MCA.MSc(IT),Mtech(IT),MPhil (Comp. Sci) Department of Computer Science, Sainik School Amaravathinagar Cell No: 9431453730 Praveen M Jigajinni Prepared by Courtesy CBSE
- 4. STRINGS
- 5. Like many other popular programming languages, strings in Python are arrays of bytes representing Unicode characters. However, Python does not have a character data type, a single character is simply a string with a length of 1. Square brackets can be used to access elements of the string. STRINGS
- 6. How to change or delete a string?
- 7. Strings are immutable. This means that elements of a string cannot be changed once it has been assigned. We can simply reassign different strings to the same name. >>> my_string = 'programiz' >>> my_string[5] = 'a' TypeError: 'str' object does not support item assignment. How to change or delete a string?
- 8. How to create a string in Python?
- 9. How to create a string in Python? Strings can be created by enclosing characters inside a single quote or double quotes. Even triple quotes can be used in Python but generally used to represent multiline strings and docstrings. STRINGS
- 11. REPRESENTATION OF STRING >>> s = “Hello Python” This is how Python would index the string: Forward Indexing Backward Indexing
- 12. STRINGS – Programming Example
- 13. STRINGS - Example Output Next Slide...
- 15. How to access characters in a string?
- 16. How to access characters in a string? We can access individual characters using indexing and a range of characters using slicing. Index starts from 0. Trying to access a character out of index range will raise an IndexError. The index must be an integer. We can't use float or other types, this will result into TypeError. STRINGS
- 17. How to access characters in a string? Python allows negative indexing for its sequences. The index of -1 refers to the last item, -2 to the second last item and so on. We can access a range of items in a string by using the slicing operator (colon). STRINGS
- 18. STRINGS – Programming Example
- 19. STRINGS
- 20. STRINGS
- 21. SLICING STRINGS EXAMPLES For example: >>>“Program”[3:5] will result in: ‘gr ’ >>>“Program”[3:6] will yield: ‘gra’ >>>p = “Program” >>>p [:4] ‘Prog’ >>>p = “Program” >>>p [4:] ‘ram’ >>>p = “Program” >>>p [3:6] ‘gra’
- 22. Index Error!
- 24. More Functionality of String
- 25. More Functionality of String >>> len(“Sainik School”) 13 >>>print(“Sainik” + “School”) Sainik School >>>print(“A” * 4 ) AAAA >>>”sa” in “sainik” True >>>”pr” in “computer” False Finding Length of string String Concatenation String Repeat Substring Tests
- 26. More Functionality of String >>> name1="computer" >>> name2=name1[3:5] >>>name2 pu String Slicing
- 27. String Methods
- 28. String Methods In Python, a method is a function that is defined with respect to a particular object. Syntax: object.method(arguments) For Example: >>>name=“Classic” >>>name.find(“s”) 3 the first position where “s” appears String object String Method Method Argument
- 29. Built in Methods
- 30. 1. capitalize() Method Capitalizes first letter of string First letter capitalization
- 31. 2. lstrip() & 3. rstrip() Methods lstrip() method is used to remove left padded spaces in a given string >>>name1=“ a “ >>>name1.lstrip() ‘a ‘ rstrip() method is used to remove right padded spaces in a given string >>>name1.rstrip() ‘ a’ Removing left spaces Removing right spaces
- 32. 4. strip() Method strip() method is used to remove left and right padded spaces in a given string >>>name1=“ a “ >>>name1.strip() ‘a‘ Removing left and right spaces for a given string
- 33. 5. lower() Method lower() method is used to convert given string in to lower case. >>>name1=“ SAINIK “ >>>name1.lower() sainik Converting in to lower case
- 34. 6. upper() Method upper() method is used to convert given string in to upper case. >>>name1=“ sainik “ >>>name1.upper() SAINIK Converting in to upper case
- 35. 7. title() Method title() method is used to convert given string in to title case. Every first chatacter of word of a given string is converted to title case. >>>name1=“ praveen murigeppa jigajinni“ >>>name1.title() Praveen Murigeppa Jigajinni In every word first letter is capitalized
- 36. 8. swapcase() Method swapcase() method is toggle the case. Meaining upper to lower and lower to upper case. >>>name1=“ PrAvEeN“ >>>name1.swapcase() pRaVeEn Every character case is changed
- 37. 9. ljust() Method ljust() method is used to add spaces to the left side of the given string >>>name1=“ Jigajinni“ >>>name1.ljust(15) ‘Jigajinni ’ Left side padded with spaces Note: string length is 9 and 6 spaces added to the left side of string
- 38. 10. rjust() Method rjust() method is used to add spaces to the right side of the given string >>>name1=“ Jigajinni“ >>>name1.rjust(15) ‘ Jigajinni’ Right side padded with spaces Note: string length is 9 and 6 spaces added to the right side of string
- 39. 11. center(width, fillchar) Method The method center() returns centered in a string of length width. Padding is done using the specified fillchar. Default filler is a space. Centered string
- 40. 12. zfill() Method zfill() method is used to fill the zero to a given string >>>name1=“ 123“ >>>name1.zfill(15) ‘00123 ’ Filling Zeros
- 41. 13. find() Method find() method is used to find a perticular character or string in a given string. >>> name1="praveen" >>> name1.find("e") 4 e is present at 4th location (first appearance) in a given string
- 42. 14. count() Method count() method is used to the number of times character or string appears in a given string. >>>name1=“praveen“ >>>name1.count(“e”) 2 2 times e appears in a given string
- 43. 15. stratswith() Method startswith() method is used check string start with particular string or not >>>name1=“praveen“ >>>name1.startswith(“a”) False Given string not starting with “a”
- 44. 16. endswith() Method endswith() method is used check string ends with particular string or not >>>name1=“praveen“ >>>name1.endswith(“en”) True Given string ends with “en”
- 45. 17. isdigit() Method isdigit() method is used check string is digit (number) or not and returns Boolean value true or false. >>>name2=“123” >>>name2.isdigit() True >>name1=“123keyboard“ >>name1.isdigit() False Given string not number so false Given string is number
- 46. 18. isnumeric() Method isnumeric() is similar to isdigit() method and is used check string is digit (number) or not and returns Boolean value true or false. >>>name2=“123” >>>name2.isnumeric() True >>name1=“123keyboard“ >>name1.isnumeric() False Given string not number so false Given string is number
- 47. 19. isdecimal() Method isnumeric(),isdigit() and isdecimal() methods are used to check string is digit (number) or not and returns Boolean value true or false. >>>name2=“123” >>>name2.decimal() True >>name1=“123keyboard“ >>name1.isnumeric() False Given string not number so false Given string is number
- 48. 20. isalpha() Method isalpha() method is used check string is digit or not and returns Boolean value true or false. >>>name2=“123” >>>name2.isalpha() False >>name1=“123computer“ >>name1.isalpha() False >>>name3=“Keynoard” >>>Name3.isaplpha() True Given string not string it contains digits Given string does not contain string It’s a string
- 49. 21. isalnum() Method isalnum() method is used check string is alpha numeric string or not. >>>name2=“123” >>>name2.isalnum() True >>>name1=“123computer“ >>>name1.isalnum() True >>>name3=“Praveen” >>>name3.isalnum() True Given string is alpha numeric
- 50. 22. islower() Method islower() method is used check string contains all lower case letters or not, it returns true or false result. >>>name2=“Praveen” >>>name2.islower() False >>>name1=“praveen“ >>>name1.islower() True Given string is not lower case string Given string is lower case string
- 51. 23. isupper() Method isupper() method is used check string contains all letters upper case or not, it returns true or false result. >>>name2=“Praveen” >>>name2.isupper() False >>>name1=“PRAVEEN“ >>>name1.isupper() True Given string is not upper case string Given string is upper case string
- 52. 24. isspace() Method isspace() method is used check string contains space only or not. >>>name2=“ ” >>>name2.isspace() True >>>name1=“PRAVEEN M J“ >>>name1.isspace() False Given string contains space only Given string not containing space only
- 53. 25. find() Methods find() method is used to find a particular string (substring) in a given string. >>>name=“Classic” >>>name.find(“s”) 3 the first position where “s” appears String object String Method Method Argument
- 54. 26. str() Method str() method is used convert non string data into string type. >>>str(576) ‘576’ 576 is number converted to string
- 55. 27 len() Method len() method is used get a length of string. >>>len(“Praveen”) 7 Gives the string length
- 56. 28 max() Method max() method is used get a max alphabet of string. >>>max(“Praveen”) v Gives max character
- 57. 29 min() Method min() method is used get a max alphabet of string. >>>min(“Praveen”) P Gives min character P because it has ASCII Value 65
- 58. 30 split() Method split() method is used split a string. Split in to several words or substrings
- 59. 30 split() Method split() method is used split a string according to delimiter. Split in to several words or substrings according to delimiter
- 60. 31 index() Method Same as find(), but raises an exception if str not found. >>> name="Sainik“ >>> name.index("a",3,5) ValueError: substring not found >>> name.index("a",1,5) 1 Value error Character found, returning the position
- 62. 32. ord() Method ord() method is used get a ASCII value for a character. >>ord(“a”) 97 97 is the ASCII value for character ‘a’
- 63. 33. chr() Method char() method is used get a character for an ASCII value. >>chr(97) ‘a’ ‘a’ ASCII value is 97
- 64. Class Test
- 65. Class Test Time: 40 Min Max Marks: 20 1. What is string? 02 2. What is forward indexing and back word indexing? 03 3. Explain any 5 string built in methods 10 4. What are character methods? Explain in detail 05
- 66. Thank You