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:
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:
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:
- 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.
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)
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:
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.
- 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-6: What would print when the following code executes?
mylist = ['Hannah', 'Grace', 'Olivia', 'Ruth']
delimiter = ''
print(delimiter.join(mylist))
- 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.
Q-7: What would print when the following code executes?
input = "Pat,Smith,girl,65 Elm Street,eat"
pieces = input.split(",")
print(pieces[3])
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