035. Split() Method

RAM Manager: Parsing /proc Output

Linux’s /proc/meminfo looks like this:

MemTotal:       16384000 kB
MemFree:         4096000 kB
MemAvailable:    8192000 kB
Buffers:          512000 kB

Aryan needs to parse these lines into usable values:

line = "MemTotal:       16384000 kB"
# Goal: get "MemTotal" and 16384000

He also needs to parse process command lines from /proc/PID/cmdline which uses null bytes as separators, and split filesystem paths for display.

His parse_meminfo_line uses split("//") instead of split("/"), and his get_words crashes with a ValueError. Fix both.

💡 Fun fact: The Linux /proc filesystem Aryan is parsing was invented in the 1980s as a way to expose kernel data as ordinary files. Every /proc/meminfo line uses split() under the hood in nearly every monitoring tool — from htop to psutil — making string splitting one of the most-executed operations on a running Linux system.

⚠️ Watch out: "a b".split(" ") (with an explicit space) returns ["a", "", "b"] — the extra space becomes an empty string in the list. But "a b".split() (no argument) returns ["a", "b"]. Beginners almost always want the no-argument version when splitting on whitespace.

🤔 Think about it: `split()` and `join()` are inverses of each other. If `",".join(["a","b","c"])` gives `"a,b,c"`, what does `"a,b,c".split(",")` give? And what happens if you round-trip a string that already contains the separator character — for example, splitting a CSV field that contains a comma inside quotes?

Learning objectives

Use split() to parse delimited strings
Use split() with no args to split on whitespace
Strip whitespace from split results

Key concepts

split()
parsing
delimiters

Try it

Concept detail

str.split(sep, maxsplit) splits a string and returns a list.

split() → splits on ANY whitespace, collapses multiple spaces, removes empty strings split(“,”) → splits on comma; does NOT strip spaces from the parts split(“/”, 2) → splits at most 2 times; the rest stays in the last element

Critical differences: “a b c”.split() → [“a”, “b”, “c”] (handles multiple spaces) “a b c”.split(“ “) → [“a”, “”, “b”, “”, “c”] (keeps empty strings!) “”.split(“”) → ValueError! (empty separator is forbidden)

Common patterns:

Parse “key: value” lines

key, value = line.split(“:”, 1) # maxsplit=1 prevents split on value’s colons

Strip each field after splitting

[p.strip() for p in line.split(“,”)]

Parse paths safely

path.strip(“/”).split(“/”) # removes leading/trailing slash before splitting

The inverse of split() is join(): “, “.join([“a”, “b”]) == “a, b”

Solution

def parse_csv_line(line):
    parts = line.split(",")
    return [p.strip() for p in parts]

def get_words(sentence):
    return sentence.split()

def parse_path(path):
    return path.strip("/").split("/")

Tests

def test_csv_basic():
    result = parse_csv_line("Alice,30,Engineer")
    assert result == ["Alice", "30", "Engineer"]

def test_csv_with_spaces():
    result = parse_csv_line("Alice, 30, Engineer")
    assert result == ["Alice", "30", "Engineer"]

def test_get_words():
    result = get_words("hello world foo")
    assert result == ["hello", "world", "foo"]

def test_get_words_extra_spaces():
    result = get_words("  hello   world  ")
    assert result == ["hello", "world"]

def test_get_words_no_valueerror():
    # split("") raises ValueError — make sure it doesn't
    try:
        result = get_words("test")
        assert result == ["test"]
    except ValueError:
        assert False, "split('') raises ValueError — use split() with no argument"

def test_parse_path():
    result = parse_path("/usr/local/bin")
    assert result == ["usr", "local", "bin"]