Strings in python

V.M.Prabhakaran, Department Of Cse, KIT- Coimbatore Problem Solving and Python Programming 1

Strings: string slices, immutability, string functions and methods, string module Problem Solving and Python Programming 2

Strings • String is a sequence of characters. • String may contain alphabets, numbers and special characters. • Usually strings are enclosed within a single quotes and double quotes. • Strings is immutable in nature. • Example: a=„hello world‟ b=“Python” Problem Solving and Python Programming 3

Inbuilt String functions • Python mainly contains 3 inbuilt string functions. • They are – len() – max() – min() • len()- Find out the length of characters in string • min()- Smallest value in a string based on ASCII values • max()- Largest value in a string based on ASCII values Problem Solving and Python Programming 4

What is ASCII values Problem Solving and Python Programming 5

Example for Inbuilt string functions name=input("Enter Your name:") print("Welcome",name) print("Length of your name:",len(name)) print("Maximum value of chararacter in your name", max(name)) print("Minimum value of character in your name",min(name)) Problem Solving and Python Programming 6

OUTPUT Enter Your name:PRABHAKARAN Welcome PRABHAKARAN Length of your name: 11 Maximum value of chararacter in your name R Minimum value of character in your name A Problem Solving and Python Programming 7

Strings Concatenation • The + operator used for string concatenation. Example: a=“Hai” b=“how are you” c=a+b print(c) Problem Solving and Python Programming 8

Operators on String • The Concatenate strings with the “*” operator can create multiple concatenated copies. • Example: >>> print("Python"*10) PythonPythonPythonPythonPythonPython PythonPythonPythonPython Problem Solving and Python Programming 9

String Slicing • Slicing operation is used to return/select/slice the particular substring based on user requirements. • A segment of string is called slice. • Syntax: string_variablename [ start:end] Problem Solving and Python Programming 10

String Slice example s=“Hello” Problem Solving and Python Programming 11 H e l l o 0 1 2 3 4 -5 -4 -3 -2 -1

Strings are immutable • Strings are immutable character sets. • Once a string is generated, you cannot change any character within the string. Problem Solving and Python Programming 12

String Comparision • We can compare two strings using comparision operators such as ==, !=, <,<=,>, >= • Python compares strings based on their corresponding ASCII values. Problem Solving and Python Programming 13

Example of string comparision str1="green" str2="black" print("Is both Equal:", str1==str2) print("Is str1> str2:", str1>str2) print("Is str1< str2:", str1<str2) Problem Solving and Python Programming 14 OUTPUT: Is both Equal: False Is str1> str2: True Is str1< str2: False

String formatting operator • String formatting operator % is unique to strings. • Example: print("My name is %s and i secured %d marks in python” % ("Arbaz",92)) • Output: My name is Arbaz and i secured 92 marks in python Problem Solving and Python Programming 15

String functions and methods len() min() max() isalnum() isalpha() isdigit() islower() isuppe() isspace() isidentifier() endswith() startswith() find() count() capitalize() title() lower() upper() swapcase() replace() center() ljust() rjust() center() isstrip() rstrip() strip() Problem Solving and Python Programming 16

i) Converting string functions Problem Solving and Python Programming 17 captitalize() Only First character capitalized lower() All character converted to lowercase upper() All character converted to uppercase title() First character capitalized in each word swapcase() Lower case letters are converted to Uppercase and Uppercase letters are converted to Lowercase replace(old,new) Replaces old string with nre string

Program: str=input("Enter any string:") print("String Capitalized:", str.capitalize()) print("String lower case:", str.lower()) print("String upper case:", str.upper()) print("String title case:", str.title()) print("String swap case:", str.swapcase()) print("String replace case:",str.replace("python","python programming")) Problem Solving and Python Programming 18 Output: Enter any string: Welcome to python String Capitalized: Welcome to python String lower case: welcome to python String upper case: WELCOME TO PYTHON String title case: Welcome To Python String swap case: wELCOME TO PYTHON String replace case: Welcome to python programming

ii)Formatting String functions Problem Solving and Python Programming 19 center(width) Returns a string centered in a field of given width ljust(width) Returns a string left justified in a field of given width rjust(width) Returns a string right justified in a field of given width format(items) Formats a string

Program: a=input("Enter any string:") print("Center alignment:", a.center(20)) print("Left alignment:", a.ljust(20)) print("Right alignment:", a.rjust(20)) Problem Solving and Python Programming 20 Output:

iii) Removing whitespace characters Problem Solving and Python Programming 21 lstrip() Returns a string with leading whitespace characters removed rstrip() Returns a string with trailing whitespace characters removed strip() Returns a string with leading and trailing whitespace characters removed

Program a=input("Enter any string:") print("Left space trim:",a.lstrip()) print("Right space trim:",a.rstrip()) print("Left and right trim:",a.strip()) Problem Solving and Python Programming 22 Output:

iv) Testing String/Character Problem Solving and Python Programming 23 isalnum() Returns true if all characters in string are alphanumeric and there is atleast one character isalpha() Returns true if all characters in string are alphabetic isdigit() Returns true if string contains only number character islower() Returns true if all characters in string are lowercase letters isupper() Returns true if all characters in string are uppercase letters isspace() Returns true if string contains only whitespace characters.

Program a=input("Enter any string:") print("Alphanumeric:",a.isalnum()) print("Alphabetic:",a.isalpha()) print("Digits:",a.isdigit()) print("Lowecase:",a.islower()) print("Upper:",a.isupper()) Problem Solving and Python Programming 24 Output:

v) Searching for substring Problem Solving and Python Programming 25 Endswith() Returns true if the strings ends with the substring Startswith() Returns true if the strings starts with the substring Find() Returns the lowest index or -1 if substring not found Count() Returns the number of occurrences of substring

Program a=input("Enter any string:") print("Is string ends with thon:", a.endswith("thon")) print("Is string starts with good:", a.startswith("good")) print("Find:", a.find("ython")) print("Count:", a.count(“o")) Problem Solving and Python Programming 26 Output: Enter any string : welcome to python Is string ends with thon: True Is string starts with good: False Find: 12 Count: 3

String Modules • String module contains a number of functions to process standard Python strings • Mostly used string modules: string.upper() string.upper() string.split() string.join() string.replace() string.find() string.count() Problem Solving and Python Programming 27

Example import string text="Monty Python Flying Circus" print("Upper:", string.upper(text)) print("Lower:", string.lower(text)) print("Split:", string.split(text)) print("Join:", string.join(string.split(test),"+")) print("Replace:", string.replace(text,"Python", "Java")) print("Find:", string.find(text,"Python")) print("Count", string.count(text,"n")) Problem Solving and Python Programming 28

Output Problem Solving and Python Programming 29 Upper: “MONTY PYTHON FLYING CIRCUS” Lower: “monty python flying circus” Split: [„Monty‟, „Python‟, „Flying‟, „Circus‟] Join : Monty+Python+Flying+Circus Replace: Monty Java Flying Circus Find: 7 Count: 3

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