9.9. Lists and strings

A string is a sequence of characters and a list is a sequence of values, but a list of characters is not the same as a string. To convert from a string to a list of characters, you can use list:

s = 'spam' t = list(s) print(t)

Because list is the name of a built-in function, you should avoid using it as a variable name. I also avoid the letter “l” because it looks too much like the number “1”. So that’s why I use “t”.

The list function breaks a string into individual letters. If you want to break a string into words, you can use the split method:

s = 'pining for the fjords' t = s.split() print(t) print(t[2])

Once you have used split to break the string into a list of words, you can use the index operator (square bracket) to look at a particular word in the list.

You can call split with an optional argument called a delimiter that specifies which characters to use as word boundaries. The following example uses a hyphen as a delimiter:

s = 'spam-spam-spam' delimiter = '-' print(s.split(delimiter))

Q-4: What is printed by the following statements?

myname = "Edgar Allan Poe"
namelist = myname.split()
init = ""
for aname in namelist:
    init = init + aname[0]
print(init)

• Poe
• Three characters but not the right ones. namelist is the list of names.
• EdgarAllanPoe
• Too many characters in this case. There should be a single letter from each name.
• EAP
• Yes, split creates a list of the three names. The for loop iterates through the names and creates a string from the first characters.
• William Shakespeare
• That does not make any sense.

join is the inverse of split. It takes a list of strings and concatenates the elements. join is a string method, so you have to invoke it on the delimiter and pass the list as a parameter:

t = ['pining', 'for', 'the', 'fjords'] delimiter = ' ' print(delimiter.join(t))

In this case the delimiter is a space character, so join puts a space between words. To concatenate strings without spaces, you can use the empty string, “”, as a delimiter.

Q-6: What would print when the following code executes?

mylist = ['Hannah', 'Grace', 'Olivia', 'Ruth']
delimiter = ''
print(delimiter.join(mylist))

• HannahGraceOliviaRuth
• Because the delimiter is an empty string (not a space) the list would join without spaces.
• Hannah Grace Olivia Ruth
• The delimiter is an empty string, not a space.
• Hannah, Grace, Olivia, Ruth
• The delimiter is an empty string, it does not add spaces and commas automatically.
• We would get an error
• This will print without causing an error.

Q-7: What would print when the following code executes?

input = "Pat,Smith,girl,65 Elm Street,eat"
pieces = input.split(",")
print(pieces[3])

• Smith
• That's pieces[1].
• girl
• That's pieces[2]
• 65 Elm Street
• The address is at position 3 in the resulting list.
• eat
• That's pieces[4]
• We would get an error
• Why would this cause an error? We can use indices to get the element at an index in a list.

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