Run-length encoding in Python

Run-length encoding: the simplest compression scheme there is.

def encode(text):
    if not text:
        return []
    runs = [[text[0], 1]]
    for ch in text[1:]:
        if ch == runs[-1][0]:
            runs[-1][1] += 1
        else:
            runs.append([ch, 1])
    return [(ch, count) for ch, count in runs]

How it works

1. Starts a run with the first character.
2. Repeats extend the current run; a new character starts a new run.
3. Returns the runs as (character, count) pairs.

Keywords and builtins used here

• def
• else
• encode
• for
• if
• return

The run, in numbers

Lines

10

Characters to type

191

Tokens

83

Three-star pace

100 tpm

At the three-star pace of 100 tokens a minute, this run takes about 50 seconds.

Type this snippet

Step 4 of 5 in Algorithms, step 54 of 72 in Language basics.

← Previous Next →