Python split() and join(): Strings to Lists and Back

Split a String into a List of Words

The split() method cuts a string into pieces and gives you a list of them. With nothing in the brackets, it cuts wherever there are spaces, so you get a list of words.

Think of it like snapping a bar of chocolate along its lines: one bar becomes a row of separate pieces.

12345sentence = "Sunny likes Python"
words = sentence.split()
print(words)
print(len(words))
print(words[0])

words is an ordinary list from chapter 9, so len(), indexes and slices all work on it.

The rules

• split() returns a new list of strings. The original string doesn't change.
• With empty brackets, it cuts at spaces, tabs and new lines.
• Extra spaces don't matter: several spaces in a row count as one cut, and spaces at the ends are ignored.

12messy = "  Rocky   and  Lucky "
print(messy.split())

No empty words, no stray spaces. That makes split() great for text that people type.

Loop over the words

Combine split() with a for loop from chapter 10 to work on each word:

12for word in "I love Python".split():
    print(word, len(word))

Common beginner doubt: "What's the difference between looping over a string and looping over split()?" Looping over the string gives you characters: I, a space, l, o… Looping over split() gives you words.

text.split() turns a sentence into a list of words.

Split on a Comma or Another Separator

Put a separator in the brackets, and split() cuts exactly at that text instead of at spaces: text.split(","). The separator itself disappears.

Think of it like a train ticket with perforated lines: you tear exactly along the dotted lines, nowhere else.

1234data = "Sunny,25,Pune"
parts = data.split(",")
print(parts)
print(parts[2])

The rules

• split(sep) cuts exactly at sep and keeps everything else, spaces included.
• Two separators in a row give an empty string: "a,,b".split(",") gives ['a', '', 'b'].
• The pieces are always strings, even when they look like numbers.

Watch the spaces after the commas here:

123fruits = "apple, banana, mango"
print(fruits.split(","))
print(fruits.split(", "))

Split on ", " (a comma and a space), or strip() each piece afterwards.

Many numbers on one line

People often type several numbers on one line. Split the line, then convert each piece with int() inside a loop:

12345line = input()
total = 0
for part in line.split():
    total += int(part)
print("Total:", total)

Avoid: adding the pieces without converting

1234total = 0
for part in "10 20".split():
    total += part
print(total)

Don't be scared of this error! It's saying you tried to add text to a number. "10" is still a string after split(), so convert it with int(part).

Common beginner doubt: "Why is '25' in quotes in the list?" Because split() only cuts text. It never guesses that a piece is a number.

split(",") cuts at every comma, and the pieces are always strings.

Join a List into a String with join()

The join() method does the opposite of split(): it glues a list of strings into one string. You write the separator first, then .join() with the list: " ".join(words).

Think of it like threading beads on a necklace: the beads are the words, and the separator is the little knot you tie between each pair.

12345names = ["Sunny", "Rocky", "Lucky"]
print(" ".join(names))
print(", ".join(names))
print("-".join(names))
print("".join(names))

The rules

• The separator goes in front: separator.join(list).
• The separator goes only between items, never at the start or the end.
• Every item in the list must be a string.
• An empty separator "" glues the items with nothing in between.

Avoid: joining numbers

12nums = [1, 2, 3]
print("-".join(nums))

"Sequence item 0" is the first item of the list. It's an int, and join() only accepts strings.

Good: turn each number into text first

Build a new list of strings with a loop and str(), then join it:

12345nums = [1, 2, 3]
parts = []
for n in nums:
    parts.append(str(n))
print("-".join(parts))

Common beginner doubt: "Why is it " ".join(words) and not words.join(" ")?" Because join() is a string method: it belongs to the separator. Lists don't have a join() method at all, and Python tells you so.

separator.join(list) glues strings together with the separator between them.

Split, Change, Join: Edit Every Word

Most text tasks follow one pattern: split the text into a list, change each piece, then join the pieces back together. Once you know it, you can edit every word of a sentence.

Think of it like a toy train: take the carriages apart, paint each one, then couple them back together.

The pattern

1. Split the text into a list of words.
2. Change each word in a loop, and append() the new word to a new list.
3. Join the new list into one string.

12345sentence = "Sunny likes tea"
new_words = []
for word in sentence.split():
    new_words.append(word[::-1])
print(" ".join(new_words))

Each word is reversed with the slice [::-1] from topic 1, but the words stay in their places.

A web address from a title

Websites turn a title into a slug: small letters, dashes instead of spaces. Here lower() changes every word at once, so no loop is needed:

123title = "My First Python Program"
words = title.lower().split()
print("-".join(words))

This very page has a slug like that in its address.

Clean up extra spaces in one line

split() ignores extra spaces, and join() puts back exactly one. Together they tidy any messy text:

12messy = "  too    many   spaces "
print(" ".join(messy.split()))

Common beginner doubt: "Why build a new list instead of changing the words in place?" Each word is a string, and strings can't change. So you make new words and collect them in a new list.

Split, change each piece, then join: the pattern behind most text tasks.

Practice: Split and join

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1. 105.Python Program to Count the Words in a SentenceEasySolve
2. 106.Python Program to Reverse the Words in a SentenceMediumSolve