Strings in Python are sequences of characters that can be manipulated and accessed using indexes and slicing operations. A string's individual characters can be accessed using indexes like str[0], with negative indexes counting backwards from the end. The length of a string can be found using len(str). Strings are immutable but their values can be reassigned. Strings can be concatenated with + and checked for substrings with the in operator. They support various quote styles and multiline strings using triple quotes.

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Python Programming Essentials - M7 - Strings

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  http://www.skillbrew.com/SkillbrewTalent brewed bytheindustry itselfStringsPavan VermaPython Programming Essentials@YinYangPavan
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  © SkillBrew http://skillbrew.comWhatis a String A string is a sequence of charactersmessage = "Welcome to Python"2
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  © SkillBrew http://skillbrew.comAccessa character in string3message = 'Welcome to Python'print message[0]print message[1]print message[2]print message[3]print message[4]Output:Welcostr[index]
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  © SkillBrew http://skillbrew.comNegativeIndexes4message = 'Welcome to Python'print message[-1]print message[-2]print message[-3]print message[-4]Output:nohtstr[-index]
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  © SkillBrew http://skillbrew.comLengthof a string5message = 'Welcome to Python'print len(message)Output:17len(string)
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  © SkillBrew http://skillbrew.comSinglequotes Vs Double quotes You can use either single quotes or doublequotes for string literals – they are the same6>>> text = 'some text'>>> text = "some text"
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  © SkillBrew http://skillbrew.comSinglequotes Vs Double quotes (2) Need to escape double quotes in double quotedstrings• Use single quotes for strings that contain double quotes>>> s = "He said "Hello"">>> s'He said "Hello"' Need to escape single quotes in single quoted strings• Use double quotes for strings that contain single quotes>>> s = 'You've got an error!'>>> s"You've got an error!"7
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  © SkillBrew http://skillbrew.comTriplequoted strings Python also has triple quoted strings available In some cases, when you need to include really longstring using triple quoted strings is useful>>> message = """This is a multi line messageuse triple quotes if the text is too long"""8
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  © SkillBrew http://skillbrew.comTriplequoted strings (2) You can also uses triple single quotes, there is nodifference between single triple quoted strings anddouble triple quoted strings>>> message = '''This is a multi line messageuse triple quotes if the text is too long'''9Triple quoted strings are also used as Docstrings which will becovered in functions
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  © SkillBrew http://skillbrew.comNotefor C/C++ Programmers There is no separate char data type in Python In Python, a character is just a string of length 1eg: text ='f'10
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  © SkillBrew http://skillbrew.comNotefor Perl/PHP Programmers Remember that single-quoted strings and double-quoted strings are the same – they do not differ inany significant way11
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  © SkillBrew http://skillbrew.comStringConcatenation12>>> 'foo' + 'bar''foobar'>>> 'foo' + 'bar' + '123''foobar123'>>> name = 'Monty'>>> last_name = 'Python'>>> name + last_name'MontyPython'+ operator is used toconcatenate strings
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  © SkillBrew http://skillbrew.comStringConcatenation (2)13>>> 'foo' + 'bar' + 123TypeError: cannot concatenate 'str' and'int' objectsstring concatenation does not works with other types
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  © SkillBrew http://skillbrew.comStringConcatenation (2)14>>> 'foo' + 'bar' + str(123)'foobar123'Use built in str() function to convert to a string
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  © SkillBrew http://skillbrew.comStringsare immutable15>>> message = 'Python is awesome'>>> message[0] = 'j'TypeError: 'str' object does not supportitem assignment>>> message = 'Python is awesome'>>> del message[0]TypeError: 'str' object does not supportitem deletion.Python stringscannot be changed
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  © SkillBrew http://skillbrew.comStringsare immutable (2)16Strings are immutable but that does not mean the variablecannot change, variable can point to anything>>> message = 'Python is awesome'>>> message'Python is awesome'>>> message = 'Python is dynamicalytyped'>>> message'Python is dynamicaly typed'
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  © SkillBrew http://skillbrew.comWhatis Slicing17slicing in Python is powerful way of extracting sub-parts ofa string, lists, tuplesUse Case:You can use slicing to extract sub-string out of astring
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  © SkillBrew http://skillbrew.comSlicing18message= 'Python is awesome'print message[0:5]print message[7:10]print message[10:17]print message[:]print message[5:]print message[:6]Outputs:PythoisawesomePython is awesomen is awesomePythonstr[start:end]start: substring starts from this elementend: end of substring excluding the element at this index
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  © SkillBrew http://skillbrew.comSlicing(2)19str[start:end]1. Slicing always returns a new string. Remember strings areimmutable2. If you don’t provide start the substring starts from the beginningof the string. eg: message[:5]3. If end is not provided the substring runs till the end of thestring4. If both start and end are missing the entire string is returned
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  © SkillBrew http://skillbrew.cominoperatorin is a Boolean operator which takes two stringsand returns True if the first string is a sub-stringof the second string, False otherwise't' in 'Welcome to Python'True'Python' in 'Welcome to Python'True'Python' in 'Welcome to Python'True20
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  Summary What isa string Access characters in a string Negative indexes Length of string Single quotes Vs Double quotes Triple quoted strings String concatenation Strings are Immutable in operator21
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  © SkillBrew http://skillbrew.comResourcesTutorial on python stringshttp://www.tutorialspoint.com/Python/Python_strings.htm Single vs double stringshttp://docs.ckan.org/en/latest/Python-coding-standards.html22
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