`split()`

Introduction

The split() method divides a string into a list of substrings based on a specified delimiter. It is the primary tool for parsing text input in coding interviews.

Whether you're processing log files, reading CSV data, or reversing words in a sentence, split() is often your first step.

How `split()` Works

If you call split() without any arguments, it splits the string on any whitespace (spaces, tabs, newlines) and automatically discards empty strings.

text = "  hello   world  \n"
words = text.split()
print(words) # ['hello', 'world']

Splitting by a Specific Delimiter

If you provide a string argument, split() uses that exact string as the delimiter.

csv = "apple,banana,orange"
fruits = csv.split(",")
print(fruits) # ['apple', 'banana', 'orange']

The `maxsplit` Parameter

You can limit the number of splits by passing a second argument, maxsplit.

text = "key:value1:value2"

# Split only on the first colon
parts = text.split(":", 1)
print(parts) # ['key', 'value1:value2']

Interview Pattern: Reverse Words in a String

A classic interview question asks you to reverse the order of words in a string, ensuring there's only a single space between words and no leading/trailing spaces.

split() and join() make this trivial.

def reverse_words(s):
    # split() with no args automatically handles multiple spaces
    words = s.split()

    # Reverse the list of words
    words.reverse()

    # Join them back together
    return " ".join(words)

print(reverse_words("  the sky   is blue  ")) 
# "blue is sky the"

Common Interview Mistakes

Mistake: Splitting by `" "` instead of `()`

When a string contains multiple consecutive spaces, split(" ") will yield empty strings in the result, which is rarely what you want.

Incorrect:

text = "a  b"
print(text.split(" ")) 
# ['a', '', 'b']

Correct:

text = "a  b"
print(text.split()) 
# ['a', 'b']

Always use split() without arguments if you simply want to separate words by whitespace.

Time and Space Complexity

Time Complexity: \(O(N)\) where \(N\) is the length of the string.
Space Complexity: \(O(N)\) to store the resulting list of strings.

Summary

split() divides a string by whitespace and drops empty strings.
split("delimiter") divides exactly by the delimiter, keeping empty strings if consecutive delimiters exist.
Use split() in combination with join() to easily parse and reformat text.

split()