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Splitting/joining strings

8.5 Splitting/joining strings

Learning objectives

By the end of this section you should be able to

  • Use the split() method to split a string into substrings.
  • Combine objects in a list into a string using join() method.

split()

A string in Python can be broken into substrings given a delimiter. A delimiter is also referred to as a separator. The split() method, when applied to a string, splits the string into substrings by using the given argument as a delimiter. Ex: "1-2".split('-') returns a list of substrings ["1", "2"]. When no arguments are given to the split() method, blank space characters are used as delimiters. Ex: "1\t2\n3 4".split() returns ["1", "2", "3", "4"].

Checkpoint

split() for breaking down the string into tokens

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Concepts in Practice

Examples of string delimiters and split() method

1.
What is the output of print("1*2*3*".split('*'))?
  1. ["1", "*", "2", "*", "3", "*"]
  2. ["1", "2', "3"]
  3. [1, 2, 3]
2.
What is the output of print("a year includes 12 months".split())?
  1. ["a year includes 12 months"]
  2. ["a", "year", "includes", 12, "months"]
  3. ["a", "year", "includes", "12", "months"]
3.
What is the output of the following code? 
s = """This
is a
test"""

out = s.split()
print(out)
  1. Error
  2. ['This', 'is', 'a', 'test']
  3. >['This', 'is a', 'test']

join()

The join() method is the inverse of the split() method: a list of string values are concatenated together to form one output string. When joining string elements in the list, the delimiter is added in-between elements. Ex: ','.join(["this", "is", "great"]) returns "this,is,great".

Checkpoint

join() for combining tokens into one string

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Concepts in Practice

Applying join() method on list of string values

4.
What is the output of the following code? 
elements = ['A', 'beautiful', 'day', 'for', 'learning']

print(",".join(elements))
  1. 'A beautiful day for learning'
  2. ['A, beautiful, day, for, learning']
  3. 'A,beautiful,day,for,learning'
5.
What is the length of the string "sss".join(["1","2"])?
  1. 2
  2. 5
  3. 8
6.
What is the value stored in the variable out? 
s = ["1", "2"]
out = "".join(s)
  1. 12
  2. "12"
  3. "1 2"

Try It

Unique and comma-separated words

Write a program that accepts a comma-separated sequence of words as input, and prints words in separate lines. Ex: Given the string "happy,smiling,face", the output would be:

    happy
    smiling
    face
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Try It

Lunch order

Use the join() method to repeat back a user's order at a restaurant, separated by commas. The user will input each food item on a separate line. When finished ordering, the user will enter a blank line. The output depends on how many items the user orders:

  • If the user inputs nothing, the program outputs:
     You ordered nothing.
  • If the user inputs one item (Ex: eggs), the program outputs:
     You ordered eggs.
  • If the user inputs two items (Ex: eggs, ham), the program outputs:
     You ordered eggs and ham.
  • If the user inputs three or more items (Ex: eggs, ham, toast), the program outputs:
     You ordered eggs, ham, and toast.

In the general case with three or more items, each item should be separated by a comma and a space. The word "and" should be added before the last item.

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