Processing a String

word = "Hello"

for character in word:
    print(character)

Lists and strings are somewhat similar since they are both a sequence of things. Strings are sequences of characters, but lists can be a sequence of anything. The key idea is that both strings and lists are sequences, which means that you can iterate over them with a For loop. When you iterate over a list, you get each element. When you iterate over a string, you get each character.

Using the split() method

text = "A multi-word string!"
words = text.split()
print(words)

text = "ONE"
words = text.split()
print(words)

text = ""
words = text.split()
print(words)

Often, instead of processing a string character by character, we want to process it word by word, or by some other chunking of characters. To make this easy, strings have a method named split. Split is an awesome method because it is easy to use. When you call the method without arguments, a list of strings is returned from the string.

For loop and Split

authors = "Alice Bob Carol"

for author in authors.split():
    print("By", author)

As demonstrated here, after we have split a string, it is easy to loop over each word. In this example, we separate each author to print them individually.

Splitting on Characters

desserts = "Apple Pie,Yellow Cake,Plum Tart"
print(desserts.split(","))

email = "[email protected]"
email_pieces = email.split("@")
print(email_pieces)

word = "Banana"
print(word.split("nan"))

If you do not pass anything to split, then it splits on any kind of whitespace: spaces, tabs, and new lines. Sometimes, we want to split on other characters. You can pass a string as an argument to split on a different character. In this example, we split on a comma (“,”), at symbol (“@”), and the string "nan".

String Iteration in Three Ways

a_string = "AD, BE, CF"

# By each individual character
for a_character in a_string:
    print(a_character)
print("----")

# On chunks of items by a separator
for an_item in a_string.split(","):
    print(an_item)
print("----")

# On chunks of items by any whitespace
for a_chunk in a_string.split():
    print(a_chunk)

Just to summarize, there are three major ways to iterate over a string. Without the split method, you iterate by character. With a parameter in the split method, you iterate by splitting the string on the parameter. And without a parameter in the split method, you iterate by splitting the string on whitespace.

Practical Split Example

# Get user input
user_input = input("Type numbers separated by commas: ")

# Split into parts
user_values = user_input.split(',')

# Process each part independently
total = 0
for value in user_values:
    value = int(value)
    total += value

print(total)

Here is an example of the split pattern in action. The first line takes a string from the user that is expected to be separated by a specific character (a comma). Then, the string is split into string values based on that character. Finally, each substring is converted to an actual integer (instead of a string full of digits) and added to the total variable. The split method is critical, because the numbers might be more than one digit in length.

Summary

• Lists and strings are both sequences, so you can index them and iterate over them the same way.
• When you iterate over a string directly, the iteration variable will take on each character, one at a time.
• You can use the split string method to turn a string into a list of strings.
  • If you pass in no arguments, the string will be split on whitespace characters.
  • If you pass in a string value, the string will be split on that string.
• To iterate over chunks of a string, split the string and then use a for loop to iterate over the resulting list of strings.