Strings

We can do things with strings

We've already seen in Data 8 some operations that can be done with strings.



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first_name = "Franz"
last_name = "Kafka"
full_name = first_name + last_name
print(full_name)

Remember that computers don't understand context.



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full_name = first_name + " " + last_name
print(full_name)

Strings are made up of sub-strings

You can think of strings as a sequence of smaller strings or characters. We can access a piece of that sequence using square brackets [].



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full_name[1]

Don't forget, Python (and many other langauges) start counting from 0.



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full_name[0]



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full_name[4]

You can slice strings using `[ : ]`

If you want a range (or "slice") of a sequence, you get everything before the second index, i.e,. Python slicing is exclusive:



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full_name[0:4]



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full_name[0:5]

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



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full_name[:5]



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full_name[5:]

If we want to find out how long a string is, we can use the len function:



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len(full_name)

Strings have methods

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



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str.

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



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str.upper?

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



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full_name.upper()

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

Don't forget, simply calling the method does not change the original variable, you must *reassign* the variable:



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print(full_name)



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full_name = full_name.upper()
print(full_name)

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



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"Franz Kafka".upper()

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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1.upper()



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"1".upper()

Challenge 1: Write your name

Make two string variables, one with your first name and one with your last name.
Concatenate both strings to form your full name and assign it to a variable.
Assign a new variable that has your full name in all upper case.
Slice that string to get your first name again.



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Challenge 2: Try seeing what the following string methods do:

* `split`
* `join`
* `replace`
* `strip`
* `find`



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my_string = "It was a Sunday morning at the height of spring."



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Challenge 3: Working with strings

Below is a string of Edgar Allen Poe's "A Dream Within a Dream":



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poem = '''Take this kiss upon the brow!
And, in parting from you now,
Thus much let me avow —
You are not wrong, who deem
That my days have been a dream;
Yet if hope has flown away
In a night, or in a day,
In a vision, or in none,
Is it therefore the less gone?  
All that we see or seem
Is but a dream within a dream.

I stand amid the roar
Of a surf-tormented shore,
And I hold within my hand
Grains of the golden sand —
How few! yet how they creep
Through my fingers to the deep,
While I weep — while I weep!
O God! Can I not grasp 
Them with a tighter clasp?
O God! can I not save
One from the pitiless wave?
Is all that we see or seem
But a dream within a dream?'''

What is the difference between poem.strip("?") and poem.replace("?", "") ?



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At what index does the word "and" first appear? Where does it last appear?



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How can you answer the above accounting for upper- and lowercase?



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Challenge 4: Counting Text

Below is a string of Robert Frost's "The Road Not Taken":



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poem = '''Two roads diverged in a yellow wood,
And sorry I could not travel both
And be one traveler, long I stood
And looked down one as far as I could
To where it bent in the undergrowth;

Then took the other, as just as fair,
And having perhaps the better claim,
Because it was grassy and wanted wear;
Though as for that the passing there
Had worn them really about the same,

And both that morning equally lay
In leaves no step had trodden black.
Oh, I kept the first for another day!
Yet knowing how way leads on to way,
I doubted if I should ever come back.

I shall be telling this with a sigh
Somewhere ages and ages hence:
Two roads diverged in a wood, and I—
I took the one less traveled by,
And that has made all the difference.'''

Using the len function and the string methods, answer the following questions:

How many characters (letters) are in the poem?



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How many words?



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How many lines? (HINT: A line break is represented as \n )



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How many stanzas?



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How many unique words? (HINT: look up what a set is)



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Remove commas and check the number of unique words again. Why is it different?



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