Strings in Python

Strings in Python are the set of characters that, once defined, cannot be changed by any other method like replace. Even if we use the replace method it still does not modify the original string that we use, but just copies the string and then modifies it, and then returns the results.

In Python we can create the strings by using single quotes, double quotes and even using triple quotes. For example:
Using single quotes:

Python 2.7.3 (default, Apr 10 2012, 23:31:26) [MSC v.1500 32 bit (Intel)] on win32
                      Type "copyright", "credits" or "license()" for more information.
                      >>> 'This is my first srting'
                      'This is my first srting'
                      >>>
                      

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Using double quotes:

Python 2.7.3 (default, Apr 10 2012, 23:31:26) [MSC v.1500 32 bit (Intel)] on win32
                      Type "copyright", "credits" or "license()" for more information.
                      >>> "This is my double quote string"
                      'This is my double quote string'
                      >>> 
                      

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Using triple quotes:

Python 2.7.3 (default, Apr 10 2012, 23:31:26) [MSC v.1500 32 bit (Intel)] on win32
                      Type "copyright", "credits" or "license()" for more information.
                      >>> '''This is my tripe quote string'''
                      'This is my tripe quote string'
                      >>> 
                      

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It really doesn’t matter what type of string we use unless we are looking to derive from the result. For example we are using something like “It’s a nice place ”, then in this case, because we have a single quote in our original string we cannot use single quotes before and after the sting.

Example:  

>>> 'It's a nice place'
                      SyntaxError: invalid syntax
                      >>> 
                      

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So to use this type of string we need to use double quotes such as below:

>>> "It's a nice place"
                      "It's a nice place"
                      >>> 
                      

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We can also use the backslash ‘\’ to run the same string with single quotes.
Example:

  
                      >>> 'It\'s a nice place'
                      "It's a nice place"
                      >>>
                      

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Similarly the example below will show how to use the backslash when we are using double quotes within a double quote string:

>>> " Sam asked "Did you get my key ?" to Hari "
                      SyntaxError: invalid syntax
                      >>>
                      

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To run this string we can use the backslash or triple quotes as shown below:

>>> " Sam asked \"Did you get my key ?\" to Hari "
                      ' Sam asked "Did you get my key ?" to Hari '
                      

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>>> ''' "Sam asked "Did you get my key ?" to Hari'''
                      ' "Sam asked "Did you get my key ?" to Hari'
                      >>>
                      

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So, how do we use a string inside a variable? Lets pass a string inside variables:

>>> x="Steve"
                      >>> y="jobs"
                      >>> x+y
                      'Stevejobs'
                      

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Just to make a little difference on the above example, let’s put a space in between the Steve and Jobs.

>>> x+'   '+y
                      'Steve jobs'
                      

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The “+” sign is used for concatenation. Without the ‘+’ symbol we cannot concatenate the strings of the variable as shown in this examples.

Now if we just add a space on the x variable like:

  >>> x="Steve  "
                       
                      

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And then run x+y the result will look as below:

>>> x="Steve  "
                      >>> x+y
                      'Steve  jobs'
                      >>>
                      

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We can also run the same variables like using a comma in between such as below:

>>> x,y
                      ('Steve', 'jobs')
                      >>>
                      

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Python converts the strings in two different ways. We have seen that with single, double and triple quotes, it displays the strings, but if we use the same examples using the PRINT command then it displays the strings as below:

>>> print "It's a nice place"
                      It's a nice place
                      >>> 
                      

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In this example we didn't get the single quotes at beginning and end of our strings. This is important to note because we can also use a number as a string. For example, say we declared a variable called n = 1269 and want it to be added to a string called “EMPID =” then what should be the expected result?

The result we are looking for will be ‘EMPID = 1269’.

We get the result like this:

>>> n= 1269
                      >>> "EMPID =" +n
                      
                      Traceback (most recent call last):
                        File "<pyshell#26>", line 1, in <module>
                          "EMPID =" +n
                      TypeError: cannot concatenate 'str' and 'int' objects
                      >>>
                      >>> print "EMPID =" +n
                      
                      Traceback (most recent call last):
                        File "<pyshell#27>", line 1, in <module>
                          print "EMPID =" +n
                      TypeError: cannot concatenate 'str' and 'int' objects
                      

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We can see that we are getting an error because the variable is a number and cannot be concatenated with strings that are characters.

So we use a n= str (1269) in place of “n= 1269”. This will only take the string of the number and then the result will be as below:

>>> n= str (1269)
                      >>> "EMPID =" +n
                      'EMPID =1269'
                      >>> print "EMPID =" +n
                      EMPID =1269
                      >>>
                      

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We can also display the string with the number, without using the str function, by putting them between a single quote. For example let us take another variable called num= 1269.

>>> num=1269
                      >>> print "EMPID =" + `num`
                      EMPID =1269
                      >>>
                      

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For more information on strings you can log on to http://python.org.