Intro to operations on strings

Loosely Based on Lecture Materials By: Milad Fatenejad, Katy Huff, Joshua R. Smith, Tommy Guy, Will Trimble, and Many More

There are operations that can be done with strings.



In [1]:

    
firstName = "Johan"



In [2]:

    
lastName = "Gambolputty"

When concatenating strings, we must explicitly use the concatenation operator +. Computers don't understand context.



In [3]:

    
fullName = firstName + lastName



In [4]:

    
print fullName









    



JohanGambolputty



In [5]:

    
fullName = firstName + " " + lastName



In [6]:

    
print fullName









    



Johan Gambolputty

You can also think of strings as a sequence of smaller strings or characters. We can access a piece of that sequence using []. Gotcha - Python (and many other langauges) start counting from 0.



In [7]:

    
fullName[0]









    Out[7]:





'J'



In [8]:

    
fullName[4]









    Out[8]:





'n'

One more gotcha - in Python, if you want a range (or "slice") of a sequence, you get everything before the second index:



In [9]:

    
fullName[0:4]









    Out[9]:





'Joha'



In [10]:

    
fullName[0:5]









    Out[10]:





'Johan'

You can see some of the logic for this when we consider implicit indices



In [11]:

    
fullName[:5]









    Out[11]:





'Johan'



In [12]:

    
fullName[5:]









    Out[12]:





' Gambolputty'

There are other operations defined on string data. IPython lets you do tab-completion after a dot ('.') to see what an object (i.e., a defined variable) has to offer. Try it now!



In [13]:

    
str.









    



  File "<ipython-input-13-58171b034407>", line 1
    str.
        ^
SyntaxError: invalid syntax

Let's look at the upper method. What does it do? Lets take a look at the documentation. IPython lets us do this with a question mark ('?') before or after an object (again, a defined variable).



In [14]:

    
str.upper?

So we can use it to upper-caseify a string.



In [15]:

    
fullName.upper()









    Out[15]:





'JOHAN GAMBOLPUTTY'

You have to use the parenthesis at the end because upper is a method of the string class.

For what its worth, you don't need to have a variable to use the upper() method, you could use it on the string itself.



In [16]:

    
"Johann Gambolputty".upper()









    Out[16]:





'JOHANN GAMBOLPUTTY'

What do you think should happen when you take upper of an int? What about a string representation of an int?



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