9.8. split and join

Two of the most useful methods involving lists and strings are the methods split and join. The split method applies to strings, and it breaks a string into a list of words. By default, any number of whitespace characters is considered a word boundary.

Example

text = "Do what you can, with what you have, where you are."
words = text.split()
print(words)
print(len(words))

Console Output

['Do', 'what', 'you', 'can,', 'with', 'what', 'you', 'have,', 'where', 'you', 'are.']
11

We can place an optional argument, called a delimiter, inside the (). The delimiter sets the characters to use as word boundaries. The following example uses the string se as the delimiter:

Example

text = "Be yourself. Everyone else is already taken."
words = text.split('se')
print(words)
print(len(words))

Console Output

['Be your', 'lf. Everyone el', ' is already taken.']
3

Notice that the delimiter does NOT appear in the result.

The opposite of the split method is join, which is used on a list. The method takes all of the elements from the list, combines them, and returns a new string value. To use join, we must give Python a connector string to place between the list elements.

Example

words = ['Hello', 'how', 'are', 'you?']
connector = '-'
new_string = connector.join(words)
print(words)

print('***'.join(words))
print(''.join(words))

Console Output

Hello-how-are-you?
['Hello', 'how', 'are', 'you?']
Hello***how***are***you?
Hellohowareyou?

Note that the original list (words in this example) remains unchanged. Also, we can use the empty string, whitespace characters (like ' ' or '\n') or multi-character strings as the connector.

9.8.1. Use split and join

These two methods are SUPER useful, since they allow us to convert between a mutable data type and an immutable one.

Try It!

Let’s put together a program that alphabetizes the words in a string.

1. On line 4, define the tools_list variable and set it equal to tools.split().

2. On line 5, print tools_list and note how each element includes a comma as part of the word. Let’s fix this.

3. Inside split() set the delimiter to be a comma followed by a space ', '. Rerun the program to verify that tools_list contains only words now.

4. On line 6, apply the sort() method to tools_list. Note that you do NOT need to assign the sorted list to a variable. tools_list.sort() is all you need.

5. Print tools_list again to verify that it is now alphabetized.

6. Next, set sorted_string equal to ''.join(tools_list), then print sorted_string.

7. The words in sorted_string are all squeezed together. Change the connector string in the join statement to be something other than the empty string. Try connecting the words with a hyphen, a comma, a space, and a comma-space to see which one looks best when printed.

# Follow the given instructions to code a program that produces an alphebetized string.
tools = "hammer, screwdriver, pliers, drill, clamp"
sorted_string = ''

repl.it

Question: Did the program change the original tools string? What can you do to find out?

Note

It is possible to alphabetize the string without using lists, but the code would be much more complicated. The difficulty comes with figuring out the proper order of words in the new string. This requires multiple slices from tools, plus conditionals to arrange the words, followed by repeated concatenation.

Placing the words into a list saves us a lot of time and effort.

9.8.2. List Type Conversion

Python has a built-in type conversion function called list that tries to turn whatever you give it into a list.

Example

test = list("Crunchy Frog")
print(test)

Console Output

['C', 'r', 'u', 'n', 'c', 'h', 'y', ' ', 'F', 'r', 'o', 'g']

The string "Crunchy Frog" gets turned into a list by taking each character in the string and making it an element in the new list. Note that the list conversion function only works on data types that consist of smaller pieces.

In general, any collection can be turned into a list using this function.

For strings, list produces a different result than the split method. split breaks a string into a list of words, while list breaks it into a list of characters.

Try It!

In the program below, lines 5 - 7 use the accumulator pattern to reverse the characters in text. Let’s use the list function to reverse other_text:

1. On line 11, define the char_list variable and set it equal to list(other_text).

2. On line 12, print char_list to verify that the function separated other_text into single characters.

3. On line 13, apply the reverse() method to char_list. Note that you do NOT need to assign the reversed list to a variable. char_list.reverse() is all you need.

4. Next, define the variable rev_other and set it equal to ''.join(char_list).

5. Print rev_other.

text = 'Taco Cat'
other_text = 'Python ROCKS!'

# Reverse a string with a loop:
rev_text = ''
for char in text:
rev_text = char + rev_text
print(rev_text)

# Reverse a string with list & join:

repl.it

Note that the print statement on line 12 is not needed for this technique to work. We just use it so see what the list() function returns.

9.8.3. Check Your Understanding

Question

What is printed by the following statements?

my_name = 'Edgar Allan Poe'
my_names = my_name.split()
initials = ''
for name in my_names:
   initials += name[0]
print(initials)

1. Poe

2. EdgarAllanPoe

3. EAP

4. William Shakespeare